The issue is first that if you will make the interaction the way that you want once you click “view assignment” all of the assignments open - not only one - that is because in CMS each item will have the same interaction…
If you want to achieve that each individual button opens only one you can do it with custom code quite easily… in fact I had a very similar issue myself and I had @sam-g help me…
check it out - it has all the code to make it work for you. LMK if you need additional help