Dear Simran,
You can refer the details from here: Fiori Apps Library
The features of this App are as below:
Display approved purchase requisitions that are not yet assigned to suppliers
Assign suppliers to a selected set of purchase requisitions
Select the relevant supplier if multiple suppliers can deliver the product
Bundle a selected set of purchase requisitions by supplier and simulate the purchase orders (one purchase order per supplier)
Review simulated purchase orders
Create purchase orders
I can see the first 2 steps are done in your case, but 3rd step is done wrongly?
Please refer the details from the link and try accordingly.
Thanks
Prem