Your post isn't clear.  I am reading it a little differently than Lisa.

If you are asking what your client, the attorney does, for a 1099NEC form received which should have gone to the law firm, this is what I would do.

First, try to have it re-issued correctly.  If they do that, problem resolved.

If that doesn't work, then I would fill out a Schedule C reporting the income so IRS matching program is happy.  Then I would subtract this same amount on the other expense line of Schedule C with the identifier "1099NEC received in error".  If you want to provide more detail, you could attach a statement explaining who should have gotten it with their tax number, which your client should have if he works for that firm.