Converting GPS coordinates to a (street) address is called reverse geocoding. This is technically quite feasible, and there are a number of websites that will do it, eg Reverse Geocoding Tool Convert Lat Long to Address. However, this feature is typically not available on (free) mobile apps because (a) it requires a live network connection to (b) a dedicated geo server running the necessary service and geo-database! So you will find that any 3rd-party websites offering an API to perform reverse-geocoding are either a paid service (requiring a token or other authentication mechanism) or if a free service they will impose a strict cap on the number of requests they’ll satisfy from a given client in a given time period. These limitations typically make it infeasible to include such a feature in a free, offline capable mobile app like Collect.
You best bet would probably be to capture a GPS location in your form, and then perform a reverse-geocode to convert this to a (permanent) address field in later processing. And if you have a very large number of submissions to process you may have to consider a paid service (or convert them individually manually using a free website, which will be tedious).
