Users can enable the Batch & Expiry for existing products by doing the following steps:
Step 1: Perform a Stock Adjustment operation and make the stock 0 of the product for which you want to enable Batch & Expiry.
Step 2: Go to Inventory Management, edit the product and enable Batch & Expiry Management for that product.
*Note: Batch & Expiry can only be enabled after changing the Stock to 0.