How to raise dunning level in a document?

I want to raise the dunning level from '3' to '4' in a document for 1 when I change the dunning from 'L' to 'N' for example. I need a simple function but I cant find it. Anybody have an idea?

I have data for debitor, document number, booking date etc..

Solution

there is no formal function modules for your requirement. You can use standard FI Substitution function which fits to your use case. Transaction code is GBB1.