There is no chat feature to enable
If you go into settings - connections - more connection settings, do you have the option to turn on rich communications?. I have found that some networks don't support chat features. My mum had to use Google messages as giff gaff didn't have chat features available in Samsung messages. If it's down to the network you can either contact and ask, or use Google messages which will have rich communications work. Sometimes it's just a case of waiting for it start working. Going to a new phone can stop it working and can take up to a few weeks. 
