Customer wants to cancel the sales order line 1.1 and 1.2 and these were already shipped in other or

Summary

Customer wants to cancel the sales order line 1.1 and 1.2 and these were already shipped in other order lines

Content

Customer wants to cancel the sales order line 1.1 and 1.2 and these were already shipped in other order lines.

1.1 Awaiting shipping and released to warehouse
1.2 manual Reservation required and with warning Another User request is being processed.

Not able to reserve and unschedule the sales order line 1.2.

also while cancelling the order 1.1 and 1.2 getting below error

You Cannot Submit The Change To Order XXXXXXX Because Other Changes Are Being Processed. (FOM-4515052)