about home address update

I just called USCIS to update my address on pending I140 petition (via PERM). But I was told that I could not change the address since I am not either the applicant or petitioner. My employer is the petitioner and I am only the benificiary. So I was told that I should ask my employer or attorney to send a letter to change the address. Is this correct? Has anybody experienced this when you tried to update your address? Thanks a lot.