I have Tabular section Productlist, it has Product Name column.
Product Name datapath is Products catalog.

I need to choose Product Name = Printer and Mouse items and they are in Computer folder of Products catalog. Let say I have chosen Printer item already.

I want when Selection Form of Products catalog is opening second time for choosing Mouse item Computer folder be opened automatically.

If you start choise Product Name in cell where value is Printer (or another), then Selection Form will be opening with focus on value Printer.
So you can add new line to Tabular section Productlist by command Copy (F9). And so when Selection Form of Products catalog is opening second time, the focus will be on value of copied line. I think, it can resolve your task.

But what was written above is also really to do by script. After first selection save value of selection and then fill Parameter CurrentRow at ChoiseForm of Products catalog

&AtServer
Procedure OnCreateAtServer(Cancel, StandardProcessing)
   LastValue = GetLastValue();
   
   if ValueIsFilled (LastValue) then
      Parameters.CurrentRow = LastValue;
   endif;
EndProcedure

You can also save the Parent of last item in a form attribute and pass it as a parameter to the choice form.