Form submissions and checking if they already exist in a board

Sorry if this is a basic question but I need some help.

We want to get course participants to register their attendance via a form at the end of a session. I want to be able to have their company linked to the form initially and then capture the attendees. How can I ensure we do not duplicate existing contacts and add the new ones too.

Many thanks in advance and please ask me any questions if I did not explain myself properly.

1