change value of combobox in a grid by code

Sorry, but I darn near fell out of my chair!

You would have to make the row the selected row. Identify the selected row. Identify the column of the combobx. Identify the selected index/value.

Secondly, if connected to another table, is it a reference table? if not, you will need to cascade the changes by starting with the primary table and then update the second table. You don't change the foreign element. You update it. You always change were the data has originated from first.