Removing members from a contact group is as easy as adding them, but on the Samsung device, you must select the edit mode to remove members.

Android 10 (One UI 2.0)
Step 1:  Open the  Contacts -App
Step 2:  Open the  menu
Step 3:  Tap on  Groups
Step 4:  Tap on desired  Group
Step 5:  Tap on  Edit
Step 6:  Tap on  Remove
Step 7:  Confirm with  Save
  1. Open the Contacts-App
  2. Open the menu
  3. Tap on Groups
  4. Tap on desired Group
  5. Tap on Edit
  6. Tap on Remove
  7. Confirm with Save

Samsung Instructions