How do you create a flow that captures quantity field and product name field from related records and populate a total for each product on account

Question

I am hopeful to find some help or guidance on how to total up partial credits by product name on an account page.

1. We have account page
2. Cases are created for an account
3. If warranted a credit request record is created for the case, which references the case number
4. The credit request record has credit lines that are created for each product that we will issue a credit for and partial quantity. The credit line references the credit request number. Example: Credit line 1 product name xxx quantity .5 Credit line 2 prodcut name yyy quantity .75
5. Instead of issuing partial credits, we would like to total these credits on the account page.
6. When the total on the account page equals a whole quantity over time, we would alert to send a whole unit and the account page quantity would be reduced. Example: If total of product name xxx account quantity equals 1.5, then an email alert would notify the team to send quantity of 1 and reduce the account quantity to .5 for that product