OPPO A57s
Turn call waiting on or off
When call waiting is turned on, you can answer a new call without ending your ongoing call.
Press the phone icon.
Press the menu icon.
Press Settings.
Press Calling accounts.
Press Advanced settings.
Press Additional settings.
Press the required SIM.
Press the indicator next to "Call Waiting" to turn the function on or off.
Press the Home key to return to the home screen.
1. 1. Find "Additional settings"
2. 2. Turn call waiting on or off
3. 3. Return to the home screen