The added members or contacts of a group or label on the OnePlus smartphone can be removed at any time.

When a group member is removed, only the contact is removed from the group, but not from the contact list.

Note: If the removed member was previously marked as a recipient in an existing group message or e-mail, he/she will not be removed from it, which means that a new conversation must be started.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Contacts app
Step 2:  Open the  menu
Step 3:  Choose a  label/group
Step 4:  Open the  menu
Step 5:  Tap on  Remove contacts
Step 6:  Tap on  Remove
Step 7:  Tap on  Quit
  1. Open the Contacts app
  2. Open the menu
  3. Choose a label/group
  4. Open the menu
  5. Tap on Remove contacts
  6. Tap on Remove
  7. Tap on Quit

OnePlus Instructions