Changing SH in VL01N

Dear Gurus,

In my client's place which is a make to order scenario, we have made an Order for a material for 2 pcs and after stock input thru 561-E (w.r.t. Sales order & Item # 10), I want to deliver 1pc to first SH and 1pc to second SH. SP has 3 SHs.

Now in VL01N I want to choose 1pc and enter first SH and do PGI and then make another Delivery for 1pc to the second SH. System is allowing to make delivery for the default SH, who was entered in the order and does not allow any one else.

How shall I change a SH in VL01N?