edit a submission

https://www.jotform.com/build/70212365908151

We encountered this problem: a registrant paid her registration fees (hotel and meals) with her credit card. A few days later, she decided to stay one more night ($100.) at the hotel and edited her submission by selecting one more day at the hotel. The total balance due showed up was the amount she already paid and this additional $100.00.

Is there a way to fix on the form so the new total can substract the amount already paid, so the true balance due is $100.00.

Thanks. 

I dont see a direct solution using the same form, a workaround can be created using https://www.jotform.com/help/97-How-to-Save-Forms-and-Continue-Later

Creating a separate form for additional payments may help.