@Ruby_Sniderman, I don’t believe that’s possible. Forms, as you’ve discovered, only create new records - they don’t allow you to edit a particular record. For edit permissions, a user would need to be a collaborator in the base (a user you pay for).
You could, however, collect responses in a table and then use a linked record field to collect those responses together. The user inputting the form would need to know the name of the linked record they’re adding onto, such as one with their name associated with it. The downside is, responses will become a very tall table very quickly.

@Ruby_Sniderman,
There are also external tools on the market that let you update existing records through forms. For example, this company makes several tools for this purpose:
But there are other companies that do this as well, such as https://on2air.com/on2air-forms/ and https://www.stacker.app