hi Syed,
What I understood in your issue that you execute this SDBONT06 and document got updated with respective agreement with customer and you want to revert back to previous state!
I have one solution that you can try:
Go to VBO2 and delete accrue amount (note: negative amount will increase the total accrual amount and positive amount will decrease the amount) and save and delete the condition and save it. The impact will be, while you run T-Code VBOF (Rebate: Update Billing Documents) accrual account will be updated with zero value.
Then again create the rebate agreement for that customer.
Let me know if it is working for you!
Thanks