Hello, you can refer to the following steps:
1. Choose Service > SDH Protection Subnet > Manage SDH Protection Subnet from the Main Menu.
2. Right-click the protection subnet to be deleted and choose Delete from the NM or Delete from the NE or Delete All from the NM from the short-cut menu.
Suggestion:
1. Delete the protection subnet from the network layer.
2. Delete the ring MSP configuration from a single NE.
3. And search for the protection subnet to ensure that the protection subnet disappears.

For more information, please click the following link:
https://forum.huawei.com/enterprise/en/question-about-the-operation-of-deleting-the-protection-subnet/thread/624255-875
Thank you!