FBL5N Adding Dunning Procedure and Accounting clerk in layout option

Hi Gurus

Plaese help me to add the field Dunning Procedure and Accounting Clerk in the hidden field option for changing layout in FBL5N

I have checked for the option of Define Special fields for finding and sorting data but it does not allow the fileds from table other than BSEG , BKPF.

Thanks

Jhanvi