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",

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