It is not possible. You cannot design databases using FM GO, It requires FM Pro or FM Advanced to make design changes.
Not inexpensive, but I solved this problem by getting a laptop and then setting up FMS on a Mac Mini at my office.
I routinely work from a LapTop and, during a design and testing session, host the database from my laptop while accessing the file from my iOS device. This is a quick and easy way to verify layouts and test scripts without having to copy a file back and forth or upload it to a server.
Once I have the latest version up and working, I then move the file to the desired location--typically by using Drop Box to copy the file wirelessly from my Laptop to my iPhone. (And I can use the same method to copy a file back to the Drop Box folder on my Laptop when I next want to play with the file's design.)
If you are new to designing for FM GO: An Old Dog learns some new tricks...