I created items without checking Serial Number feature and started using ERP but now I can see that I can’t enter serial number of Items so how could I set on that feature of all items?
Customize item master, make it allow on submit. Check has serial number from item master. You can add serial number. After checking all the item, feel free revert the customization.
You mean, I can check this option of existing items as serial number option is looking lock.
You can only check the option as long as you haven’t done a stock transaction (like a receipt, transfer, delivery, etc).
In case you have, you can either cancel those transactions or
Stock out the current item
New stock entry receipt with serialzed inventory option enabled.