Add Column on FBL3N

Hi Experts,

I have a requirement to add a new column to the FBL3N GL Account Line item report. The New Column that needs to be added is Customer Number. I can easily add this column on our QA but it's greyed out on our Production system. May I please know if there are available configurations for this? Or how to create a new layout?

Thanks,

Mr. Stifler