How to automatically check the MEPO1211-UMSON (Free indicator) in ME21N

Hi,

I'm new in ABAP and currently I am working with the free indicator in ME21N. I have already read all the message with regards to MEPO1211 and I can't use it to make the free indicator in ME21N automatically tick and grayed out. Is there any user exit that I can use for MEPO1211-UMSON?

Hope you can help me on my problem.

Thank you.

Neil