Hi..
I have received Similar question like yours.
The best solution is that after you reverse all other module’s documents connected to co-pa documents which have wrong value, you generate all other module’s documents again.
But It is very difficult to do so realistically often.
So, If you don’t want to have an impact on other modules, you need to solve the problem using only co-pa transaction.
My solution is as follow.
1.You get the actual line item with wrong value using t-code ke24.
2. You create actual line item with minus value to have a zero for value field with wrong value
using t-code KE21N as below picture.
3. After you check whether the value field with wrong value is zero, you create actual line item
with accurate value using t-code KE21N.