Default cursor position in a new row on a Custom Tab

I have a Performance Custom Tab that we use to enter sales data from third party agencies. This requires using "Add" to enter multiple rows, with each row comprising 5 columns of data.

All works as expected except for one issue.

When I click Add to enter a new row the cursor lands in the column that the cursor was in on the previous row, which in normal data entry processes is the last column.  This then means the operator has to manually select the first column in the new row, or shift-tab to move backwards.

But what I want is that when adding a new row the cursor is always in the first column. Any ideas?

Thanks all