To (freely) quote Obelix from another thread: Do you want the answer, or do you want to learn?
If the latter, here is something to help you on your way.
It all depends on how you read the challenge.
If all you want to do is choose the user's preferred currency symbol for him/her, (assuming you know what it is), all you have to do is review the lesson, and the answer will be staring you in the face. This is how I understood the challenge, and it is really easy to do.
(Do you perhaps copy the code from the lesson into your project? Then the solution would be easy to miss. Or do you enter it manually? You should!)
If, however, you read the challenge as: Let the user choose the currency symbol while using the app, then you will need to create some dialog. Ask yourself: How would that look like? Maybe you want to let the user choose from a list you provide. What type of view do you know that allows you to do that? Or maybe you want to do it differently. It is up to you.
Good luck.