How can I populate a complete form validating if its previously in my database

Here i explain:

I have a participant registration form for a promotion and I want that if a participant is already registered in the form, you do not have to fill out the completed form again, but only have to put your email or your id and it is valid if it is already in the database of records in the form and complete all the fields automatically. How can I do it?

We do not have a feature where you can connect external databases and fetch the data in it.

But here's a workaround for that.

You can export the data from your database into an excel file and then use this widget https://widgets.jotform.com/widget/spreadsheet_to_form to search an ID and populate the data to the fields when the ID matched within the excel data.

Here's a guide on how to use this widget: https://www.jotform.com/help/442-How-to-Use-the-Spreadsheet-to-Form-Widget

If you need further assistance, let us know.