Lookup and select from another object

I have a database with objects:



There are more but these are the relevant ones.

I then have a Page in Athlete called ATP. This page pulls data from Events and some of the other Objects. It is a means of me seeing all the relevant info about this athlete in one place.

What I want to be able to do is to look up my events table and add an event to the athlete, that may be already created for another athlete. If its not then to create one.

I can create the event and link it to the athlete but i can't figure out how to lookup in the table with all the events and link it after creating the event.

Athletes to Events is a many to many relationship. Many athletes can do the same event, and athletes can do many events.

Any help gratefully received thanks.