If you have already paid your share to someone, you just need to delete the corresponding row. Swiping the row shows two options:
Pay off: meaning they are settled and the debt is paid in full
Amount: meaning just a give amount is paid
Note: Depending who owes who, the amount goes to the person who has to get paid.
Tom owes Bob $10.46.
If you swipe the row and tap Pay off, that means Tom paid Bob $10.46
If you tap amount, it asks for the amount. This means Bob paid Tom the amount you entered.
These two people will be paid off.
Note1: Select Pay off or Amount if the money is physically given or received.
Note2: The arrow shows the direction of the payment.