In addition to the option to delete an entire conversation in the Messages app on the OnePlus smartphone, we can also delete individual messages contained in it.

Note: Deleting a message only affects your own device, and does not affect the message on the chat partner's device.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Messages app
Step 2:  Choose a  conversation
Step 3:  Tap and hold a  message
Step 4:  Tap on  Delete
Step 5:  Confirm with  Delete
  1. Open the Messages app
  2. Choose a conversation
  3. Tap and hold a message
  4. Tap on Delete
  5. Confirm with Delete

OnePlus Instructions