1 – Check your current settings.
This is important to retain 3G data when moving out of 4G range. You can find this under Settings > Tethering & Networks > Mobile Network > Network Mode
If you don’t see LTE listed there, then proceed to step 2. If it’s there, select it. Failing that then you have a different problem.
2 – Go to your dialer and paste *#*#4636#*#*
Alternatively, you can use the 4G LTE Switch app to skip to step 4.
3 – A Menu Will Display Automatically
Click on Phone Info and scroll down to where it says Pick Prefered Network Type.
4 – Press the drop down box and select the option that adds LTE along with your old options.
E.g. for me before it said GSM/WCDMA, so now I pick LTE/GSM/WCDMA to turn on 4G
5 – Your network will reconnect and you should
now see a 4G icon appear in the top bar.
Note – Rebooting your phone or navigating back to Settings > Tethering & Networks > Mobile Network will reset your connection to default, meaning that you will lose 4G and have to start again! I have no idea why this is an issue, it’s ridiculous. By there you go, hope that solves your problem.