Xiaomi Redmi Note 5 cannot connect to LG FH2 speaker since there's a Bluetooth profile incompatibility
The Bluetooth profiles are an integral part of the Android system installed on your device (like a driver). Therefore usually you can't "install" or "update" the Bluetooth profiles. 

Therefore you have only two possibilities:


Buy a different speaker that supports a Bluetooth profile your phone supports.
Search the Internet if there is a different ROM available for your phone that has A2DP support.