Setting 4G LTE only.
There are many apps in order to force network setting to get 4G only.
1. Open Play store
2. Search app with key word: 4G LTE only Switch
I choose 4G LTE only Switch App from Alanpro
3. Install it
4. Open the App,
5. Tap the FORCE 4G/3G/2G
6. Scroll down to find the option: Set preferred network type: , then choose: LTE only.