By default, your Huawei device always searches for the network domestic to your country. If you are near a border or live in a rural area, your device might chooses foreign nets to provide a a better reception. To choose a network manually, you need to deactivate the network search which is activated by default.

Android 10 | EMUI 10.0
Step 1:  Open the  settings
Step 2:  Tap on  Mobile network
Step 3:  Tap on  Mobile data
Step 4:  Tap on  Carrier
Step 5:  Activate or deactivate  Automatic
Step 6:  Confirm with  OK  and choose a  Network  after
  1. Open the settings
  2. Tap on Mobile network
  3. Tap on Mobile data
  4. Tap on Carrier
  5. Activate or deactivate Automatic
  6. Confirm with OK and choose a Network after

Huawei Instructions