Create a search function that will pull existing records

Create a search function that will pull existing records

Situation:  I am allowing users to enter membership data. But, if a membership record already exists, I would like for them to search for it and then be redirected to an 'edit' page where they can edit that existing record.  I'm not sure how to do this. 

What I tried: I made a 'search' box where 'on user input' it searches for any record with the information entered and populates the form with the record information.  BUT it will save a duplicate copy if you submit it...that's my dilemma.

Any help is appreciated!