How do I make my phone 4G only?

Dialing*#*#4636#*#* or *#36446337#: In both modes you should access Networks and set a Preffered Mode from the menu to LTE only (or whichever mode your prefer at that time).1 May 2019

Method 1 — Using 4G Only Mode Code

You can’t disable 4G+ but you can choose and lock a specific 4G band. You need to root your device for that. In Qualcomm smartphones you can download “Network Signal Guru” app from Play Store then give root permission to lock a band and get rid of 4G Plus .