I'm using the Apple sign in button with custom frames but the thing is I couldnt add icon on it. Here is the code:

 SignInWithAppleButton(

                        //Request
                        onRequest: { request in
                            let nonce = randomNonceString()
                            currentNonce = nonce
                            request.requestedScopes = [.fullName, .email]
                            request.nonce = sha256(nonce)
                        },

                        //Completion
                        onCompletion: { result in
                            switch result {
                                case .success(let authResults):
                                    switch authResults.credential {
                                        case let appleIDCredential as ASAuthorizationAppleIDCredential:

                                                guard let nonce = currentNonce else {
                                                  fatalError("Invalid state: A login callback was received, but no login request was sent.")
                                                }
                                                guard let appleIDToken = appleIDCredential.identityToken else {
                                                    fatalError("Invalid state: A login callback was received, but no login request was sent.")
                                                }
                                                guard let idTokenString = String(data: appleIDToken, encoding: .utf8) else {
                                                  print("Unable to serialize token string from data: \(appleIDToken.debugDescription)")
                                                  return
                                                }

                                                //Creating a request for firebase
                                                let credential = OAuthProvider.credential(withProviderID: "apple.com",idToken: idTokenString,rawNonce: nonce)

                                                //Sending Request to Firebase
                                                Auth.auth().signIn(with: credential) { (authResult, error) in
                                                    if (error != nil) {
                                                        // Error. If error.code == .MissingOrInvalidNonce, make sure
                                                        // you're sending the SHA256-hashed nonce as a hex string with
                                                        // your request to Apple.
                                                        print(error?.localizedDescription as Any)
                                                        return
                                                    }
                                                    // User is signed in to Firebase with Apple.
                                                    print("you're in")
                                                }

                                            //Prints the current userID for firebase
                                            print("\(String(describing: Auth.auth().currentUser?.uid))")
                                    default:
                                        break

                                            }
                                   default:
                                        break
                                }

                        }
                    ).frame(width: UIScreen.main.bounds.width * 0.18, height: UIScreen.main.bounds.height * 0.08).signInWithAppleButtonStyle(colorScheme == .dark ? .white : .black).cornerRadius(16)

Apple have very strict guidelines with using Sign In With Apple.

You should go to Sign in with Apple Button and download the files that you will need.

@NigelGee I know that Apple has strict guidlines but how will I add the icon in code?

Try using this modiflier .signInWithAppleButtonStyle(.black). Think you need to do a frame as it seem to take up the whole view

struct ContentView: View {
    var body: some View {
        VStack {
            SignInWithAppleButton(.signIn,              //1 .signin, or .continue or .signUp for button label
                  onRequest: { (request) in             //2
                    //Set up request
                  },
                  onCompletion: { (result) in           //3
                    switch result {
                    case .success(let authorization):
                        //Handle authorization
                        break
                    case .failure(let error):
                        //Handle error
                        break
                    }
                  })
                .frame(width: 200, height: 50)
                .signInWithAppleButtonStyle(.black) // .black, .white and .whiteOutline
        }
    }
}

PS you might want to add this as button does not change with light/dark mode

@Environment(\.colorScheme) var colorScheme
// … code
.signInWithAppleButtonStyle(colorScheme == .light ? .black : .white)