Caluculate user meta

Hello Top team! How are you?

I know there are manny ways to do a calculation, but let me explain. We have yoga bussines with cards to buy with lesson credits. And when user buys card for exampe 5 credits and they have still 2 credits left it would be useful Fluetn Cart could calculate it. So it maps 7 credits to the user.

Also was trying with Fluent Crm Pro,
For the moment i have to stick on Uncanny automator.

Thank you and have a great day.