For example, if we are abroad for business reasons or on vacation, the OnePlus smartphone automatically dials into a foreign network.
If reception in this provider network is rather poor, we can select the network manually. In this case, the automatic system is switched off and all available networks are searched for, so that we can then select the network ourselves.

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  Network operators
Step 6:  Disable  Choose automatically
Step 7:  Confirm with  OK
Step 8:  Choose an available  network
  1. Open the Settings
  2. Tap on Wi-Fi & network
  3. Tap on SIM & network
  4. Choose a SIM card
  5. Tap on Network operators
  6. Disable Choose automatically
  7. Confirm with OK
  8. Choose an available network

OnePlus Instructions