It works! Thanks @ClarkWalliser - if anyone else is reading this and needs a little more info:
So the entity in this case (looking in DFDM MAS90\providex.ddf) is: IM_PHYSICAL (if you switch the Key No to By Name and search Physical it will pull up a short list for you. Select IM_Physical and then switch the Key No. back to Primary Key - which is the number you have to look for in DFDM MAS90\providex.dde - find the Key # and there will be a bunch of additional fields tied to that key, find the QuantityonHand field and open and follow Clark's instructions - edit field 20 (15,1) and change to 0. After that you'll see the Qty on Hand field on the IM.Physical import data tab.