Update forms new record

[jeremy0028]

I have a table and form called payments in the table i have th
following

Tranasaction ID(Auto Number)
Payment posted on
Patient account
Date of service from
Date of Service to
Procedure
Modifer
fee
Insurance payment
Patient payment
Copay payment
Adjustment
Balence = Fee-Insurance payment-patient payment-copay payment
adjustment

I also have a table and form called add charge which has the following

Patient Account
Date of service from
Date of Service to
Procedure
Modifer
fee

I created and append query to link the fields to the add payment
table

It looks somthing like this

Main form patient account(Combo Box)

Subform(Datasheet View)

Transaction ID Date of service from date of service to procedure mo
fee insurance pmt

the you should figure out

I created a command button called add new payment on the main form
I select the patient account in the subform displays dates of service
i enter 35.00 in the insurance payment field where the payment amoun
is suppose to go to the correct date of service but lets say
recieved another payment from the insurance at a latter date for th
same date of service. I click new payment select patient account
still displays orignal amount posted.

How do i show that when i press new payment so the field calle
insurance payment will read 0.00 so i could enter a new payment for th
same date of service