How to trigger a flow based off previous form submission data

There is a trigger for flows called "Form Submission Data", which works off the most recent form submission for that contact.

You can choose the form as part of the trigger.

Then realistically, you're either going to do something to all those contacts, or use a condition to filter them to do certain actions.

Next, once you've saved and published the flow, go to Contacts/Database and add the contacts to the flow.