Reservation on lines of Service Item Worksheet

In the service item worksheet lines, there are the standard reservation fields, but I do not see a way to reserve the lines (other than from a purchase order). Any idea how I can reserve items on the worksheet?

Hi, On the sales order ,I can do it by function—> reserve on the purchase order ( even i don’t try it ) I can see it also On Req. work sheet also fuction —> reserve Can you indicate more precisely about the workseheet you are working on?What do you mean by service item worksheet lines. Hoping that I am helping . Rgds, Jouhayna