Wrong expenses encoded in FO-food PAF form

After we in LCR encoded many PAF forms about COVID-19 FO help, we discovered that we made a mistake about the amounts we encoded. (sample: encoded amount was 1250 but has to be 1050). The expenses had then already approved. Is there a way to change only the expenses or do I have all to void and encode again. If I click the ref# in the Expenses Summary I can make a choice between void and adjust expenses. If I click on Adjust I can not change any. If I do I got an error.

Any step by step solution would be very welcome.