Hello Rebeccatai,
Welcome to the Community page,
If you don't see the option to do a credit note in the app then it is not available and you will have to do it on the web browser of QB instead.
As the app is limiting on the things you can do in it.
You have clicked a link to a site outside of the QuickBooks or ProFile Communities. By clicking "Continue", you will leave the community and be taken to that site instead.