Let me help you record the deposit by check when receiving cash back, @Sabailey.
Cashback is the money that you receive back from a transaction. To record this, use a bank deposit and enter the details for the check and the cashback.
Here's how:
Go to New +, and from the Other section, select Bank Deposit.
In the Choose an Account dropdown, choose the bank account where you receive the check and cashback.
Enter the check details and amount in the first row of the Add Funds to Deposit section.
On the other row, enter the cashback details and the amount.
Regarding what specific source (from) account you need to use, I recommend consulting your accounting professional for accurate tracking. If you don't have one, you can find a professional through this link: Find an accountant.