Sorry, it's my fault, I missed something about Root permissions. This is the corrected answer.
Fortunately, I solved this problem today, but I don't understand why Microsoft hides the delete button in OEM UI.
Solution:
If you have Root permissions, use Activity Manager and enable "Show not exported activities" in Setting, then view Windows Phone Link, search for activity title in the picture, and then delete the ones you want to delete, Enjoy~. : )
If you don't have Root permissions, you may need to find other ways. I recommend using Shizuku, activate Shizuku using ADB, then grant permission to RootActivityLauncher, then search for "com.microsoft.appmanager.ext2.devicemanagement.Ext2AccountDevicesActivity" at the bottom, and then you can launch it.