If I am not wrong, you would need to add them as a contributor in settings. Turn on Share and Permissions and share the feedback project with the people you want to make assignees

Then from the overview table when you edit the feedback you will be able to edit the assignee from the drop-down
Hope this helps. I am not sure if this is what you were looking for. You will find more about the frontline feedback here.
https://basecamp.qualtrics.com/utilizing-frontline-feedback

Thanks for this, however in my project it hasn't been shared with anyone and there are names in the list that were not added as contributors so there is more to it then just adding as a contributor. The answer I got from support is that anyone who has been added as a user on the brand will be populated into the list automatically - which is not ideal and should not be the case for frontline feedback projects.

afrerichs If you haven't already, I’d recommend reviewing this support page on managing feedback to help you get started. If you still have questions after reviewing the linked support pages, you'll want to reach out to the  Support team, as they are best equipped to help answer questions and provide support!

KatF thanks for this I have reviewed the support pages and unfortunately, they do not provide the answer I need. This has turned into a product idea which I have submitted. An ideal situation would be that a list of assignees should be customized to a group of users who will be addressing the feedback submitted.