How to force 3G on Android Mobile phones?

On some Android phones, "WCDMA only (read 3g)" is not specifically selectable under "preferred network type ". This is also the case on Xiaomi Redmi Android phones. Only the following options are available :
1. Prefer LTE (4G)
2. Prefer 3G
3. 2G Only

The above options are fine except for the word "prefer",

which will not force the phone to stay on 3g/4g if network signal is weak.

No option to force 3G

To force your Android phone to choose 3G,  do the following :

1. Open phone dialer and type *#*#4636#*#*
2. Select the phone information1 (sim 1) or phone information2 (sim 2)

3. Scroll down and look look for Set preferred network type
4.Tap and select "WCDMA only" from the options.
5.Tap back key to exit.

That's it.

The phone data signal will drop for sometime and come back with 3G.

Forced 3G on Android phone and lost all network signal 

If there is no 3G network available at all, the phone's signal may be lost, including calls. The phone will show a cross mark in the network signal display. In that case, the Android phone will not be able to make calls or receive calls too. If this happens, revert back tonas it was - change settings to use "prefer 3G" or 2G only.

1. Open phone  settings
2. Mobile Networks
3. Change preferred network type to "prefer 3G" or use 2G.