Hi,
You have three options in SAP to select the Po number in ME22N.
1) Go to ME22N, Menu bar select purchase order ----> other purchase order
Image may be NSFW.
Clik here to view.
2) select directly button other purchase order (shift+ F5)
Image may be NSFW.
Clik here to view.
3) click on document overview , select overview ---> purchase order and enter your purchase order number and execute . and select po number and click on copy button.
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.
Image may be NSFW.
Clik here to view.