Although the instructions on how to enable it may be obscure, both iPhone and Android phone have built-in support for TTY/TDD/TT.
The web page referred to by the Lufthansa Social Media team include a Canadian TTY/TDD/TT phone number, and instructions on how to use it.
It appears that the Lufthansa social media team could have provided clearer instructions, and the customer could have taken some initiative to remedy the situation.
