The access point names (APNs) are necessary to use the mobile data and MMS services on the OnePlus smartphone.
Normally, we receive the APN settings automatically or via configuration message as soon as a new SIM card is inserted into the device and registered in the respective provider network.

In case the access points are incorrect or are not received automatically, we can add them manually.

Note: Many network operators also offer an overview of APNs (Access Point Names) on their own website.

Android 10 | OxygenOS 10.0
Step 1:  Open the  Settings
Step 2:  Tap on  Wi-Fi & network
Step 3:  Tap on  SIM & network
Step 4:  Choose a  SIM card
Step 5:  Tap on  Access Point Names
Step 6:  Tap on  Add
Step 7:  Enter the appropriate  data  
Step 8:  Open the  menu
Step 9:  Tap on  Save
  1. Open the Settings
  2. Tap on Wi-Fi & network
  3. Tap on SIM & network
  4. Choose a SIM card
  5. Tap on Access Point Names
  6. Tap on Add
  7. Enter the appropriate data 
  8. Open the menu
  9. Tap on Save

OnePlus Instructions