If you need it all on same list as the source here is what I would do ( The following example I have just set up in a test powerapps of my own and it works very well.)
Make a choice column in your Sharepoint datasource, set its choices to 1,2,3,4,5, to be safe select allow multiple and allow custom. Should not need that but it doesn't hurt to have them selected as long as you are the one coding the entries and it is only used with powerapps it cant be done wrong.
place the following in OnSelect of a button in your gallery by the rating
ClearCollect(standbyCol,ThisItem.LocalAssignment);
Collect(standbyCol,{Value:Rating2.Value});
UpdateIf(MasterSubAreas,ID=ThisItem.ID,{LocalAssignment:standbyCol})
My sharepoint list is MasterSubAreas & LocalAssignment is the column where I have set up a choice column
This code is placed on a button in the gallery and collects the item, then collects the rating, then updates the original splist items choice column to include both what was there before, and what you have added to it. This gives you a record of every rating submitted for said item in your splist
