In addition to automatic network selection, the network can also be selected manually on the Samsung device. manual network selection is recommended, especially near the border or abroad, to avoid further costs.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Connections
Step 3:  Tap on  Mobile networks
Step 4:  Tap on  Network operators
Step 5:  Tap on  Select manually
  1. Open the Settings
  2. Tap on Connections
  3. Tap on Mobile networks
  4. Tap on Network operators
  5. Tap on Select manually

Samsung Instructions