Touch the Tools icon at the upper right and touch Find & Replace:
To find a word, type it into the first field at the top of the screen and touch the right-pointing arrow at the upper right to find the next occurrence:
To do a find and replace, into the first field enter the word to be replaced and into the second enter the word that will replace it:
Touch the right-pointing arrow at the far right to find the next occurrence of the first word and if you want to replace it, touch Replace.
Note that Final Draft Go does not have the ability to do a global find and replace.