The time zone is automatically selected by the Huawei smartphone. The device uses the data of the network in which it is located. If you want to change the time zone, the automatic search for date, time and network must be deactivated.

Android 10 | EMUI 10.0
Set time zone -  Open the  settings
Set time zone -  Tap on  System & updates
Set time zone -  Tap on  Date & time
Set time zone -  Deactivate  automatic
Set time zone -  Tap on  Time zone
Set time zone -  Choose a  time zone
  1. Open the settings
  2. Tap on System & updates
  3. Tap on Date & time
  4. Deactivate automatic
  5. Tap on Time zone
  6. Choose a time zone

Huawei Instructions