RMA- How to change the part

Dear experts, User has created RMA with one Receipts line. RMA Disposition also done against that RMA. Now RMA status is Closed refer to below screen

User has wrongly seleted the wrong part, could you please suggest me how to change the part?

You can select the wrong part on the disposition and delete it. Go back to the RMA processing screen and delete the receipt of the part. You should then be able to change the part.

When we are trying to delete the RMA Disposition, system is throwing below error