Okay, I kind of figured that part out, but I am not really a programmer so I do not know exactly how to tell it to exclude. I do have an Unique ID Field that can do be the identifier, could you tell me what to write to exclude.
Here is my SQL:
UPDATE [Daily Activity-Millennium] SET [Daily Activity-Millennium].AVAILABLE_INV = (DLookUp("[AVAILABLE_INV]","Daily Activity-Millennium","[DailyID]=" & [DailyID]-1))+[MEOH_MILLEN]-[TOTAL_TAKE];