Change ownership of a related collection

The idea is for the app to automatically classify a customer as they go shopping. I have a collection called a level, which has scoring, weight, image properties and a relationship with the user collection. Remembering that each purchase is multiplied by a weight that is in the classification. This score is added, which automatically classifies the customer / user to a level according to the score range that is in the level collection. I’ve tried all the ways but I can’t. Could someone help me?

Which part are you struggling with? Can you share some screenshots?