Before uninstalling Final Draft Go from your iPad or iPhone, use iOS's Files app or iTunes to back up all of your scripts to your cloud storage service or your computer.
To remove the app, touch and hold the FD Go icon and choose Remove App:
Next, confirm the deletion...
...and the app will be removed.
To reinstall. log into the App Store with the same credentials with which you purchased the app originally, do a search for "Final Draft Go" (without quotes) and choose Install.