Your query is not clear.. You mention
"Since in my case the shippment process i.e creation of shippment by VT01n has not been created because the route was not selected in outbound delivery and the PGI and Invoice was also done but now the user want to complete the shippment but the system is not allowing it."
If route was not proper ' eligible to transport' than your delivery will not create shipment. If you already did PGI and invoice than shipment not require as delivery is not relevant for transportation.
In case you need to do transportation than reverse invoice, correct route in delivery and than try.
Regards