When I hit Submit button the form I want the Qty that is entered into it to be added to the field in ProductsT called StockQty.
A simple SQL statement in VBA will do that for you. In the code behind you Submit button you could have something like this:
Code:
Dim SQL as string
SQL = "Update ProductsT set StockQty = StockQty + " & me!Qty & " where ProductID = " & Me!ProductID
Currentdb.Execute SQL,dbfailonerror
The where clause " where ProductID = " & Me!ProductID is necessary to identify the one record in table ProductsT that you want to update with a new quantity.
This assumes that the field ProductID in the table is unique for each record; it might be the Primary Key of the table.
It also assumes that you have a field on the StockDataEntryF form that holds the ProductID.
Replace the names in italics with the actual names of the fields in the table and on your StockDataEntryF form.