To process your orders with picklist as your starting point, you will have to create batches of shipments compulsorily.
So basically you have to follow these steps:
1- Add shipments to a batch.
2- Create a pick list for a batch. For this you have to create a picklist manually and then apply filter for the given batch ID and add all the filtered products to a picklist.
3- Create the pick list for all the filtered shipments.
4- The Shipments’ status will be “To be picked”. You will Receive the Pick list from the same page. The Shipments’ status will be “Picked”.
5- On the Shipments page, filter out the batch number and process the shipments as you have always been doing!