Using Forms, i want to populate the unique field with multiple fields from the form

Your software
My Mautic version is: v4.4.5
My PHP version is: 7.3.22
My Database type and version is:

Your problem
My problem is:
I am using the form facility in mautic as a subscription form, the details are injected into the database, this works;
first name, last name, email etc all works as expected.

I also have a unique field that is "first name, last name, email "

How do i populate this field with multiple field data, any ideas?

Please explain in detail so I can help you out.