User input dialog - how to select from a list/passing reference of object

Hello,

I'm stuck on a seemingly simple task - this is what I'm trying to achieve: A user working on a tender should be able to populate a text from a template.

1. User working on a tender click on button "get template text"
2. Show pop up with templates
3. User select template and click "select"
4. The text of the selected template is copied to the tender
5. User return to the original page.

1-3 is easy but how to I pass a reference to the Tender in step 4?

A user is associated to multiple Tenders ans multiple Templates.

Thanks :) Fredrik