Is it possible to automatically reset the Unique ID after a certian number of submissions?

Is it possible to automatically reset the sequence (submission) number after a certian number of subnissions?

I'm afraid there's no automatic solution for that. If you're going to use Unique ID to count the number of submissions and want to reset it back to zero, you will have to manually reset the current index number in the Unique ID settings.

Here's how to Add Custom Unique IDs to your Form Submissions

If you like, you can limit the number of submissions in your form. Guide: How to Limit Submissions in a Form