You can go to the Google Play Console→Order Management→Choose an order and refund it.
If the developer chooses a refund with revoke, the purchased receipt will be cleared and the user will not continue to own the item, but the user can purchase the non-consumable product again.
If the developer chooses a refund without revoke, the purchased receipt will not be cleared and the receipt will be sent when the user first initializes the IAP and is verified as a valid receipt. This means that even if a refund is made, the user will still own the item and the user cannot purchase the non-consumable product again.
What I typically do is configure several test users, and each can make a non-consumable purchase. Another approach is to simply create several similar products.