Samsung Galaxy Tab S9+
Selecting network
You can set your tablet to select a network automatically or you can select a network manually. If you select a network manually, your tablet will lose network connection when the selected network is out of reach.
Slide two fingers downwards starting from the top of the screen.
Press the settings icon.
Press Connections.
Press Mobile networks.
Press Network operators.
Press the indicator next to "Select automatically" to turn off the function and wait while your tablet searches for networks.
Press the required network.
Press the indicator next to "Select automatically" to turn on the function.
Press the Home key to return to the home screen.