Step 1: Add product with batch.
Please refer below mentioned article.
Step 2: Create purchase order by adding batch item.
Step 3: Convert Purchase order to Purchase.
Please refer to the below mentioned article.
Step 4: Click on the Purchase Order option in the left hand side.
Step 5: Select the purchase order and click on three dots, on the right hand side corner.
Step 6: Click on Convert and Click on Convert To Purchase option.
Step 7: Click on Convert to purchase. You will see the screen on that the Quantity option will be there remove the quantity.
Step 8: After removing the quantity one pop-up will appear on your screen.
Also you can select the exiting batch.
Step 9: Also you can add the new batches from the right up side corner and save the details.
Here, mention the new batch details.
Step 10: Your all details will display here and you can click on Done option.