Error while trying to modify standard memo lines LOV

On standard AR transaction lines form, there is a description field. I want to modify LOV of this field.
standard form is ARXTWMAI. i opened this .fmb in forms builder but I was unable to see the block name, LOV name.

Most closest I was able to found is 'AR_MEMO_LINE' LOV on ARXTWLIN.
But while trying to modify 'AR_MEMO_LINE' LOV, I get can not replace group; columns don't match LOV error.
I am using create_group_from_query standard utility.
According to error I tried to debug. But the source query data types, column sequence exactly matches with the query on which I have created record group.