Hello,
There are no Tamil lessons in the GNU Typist package and
I am not aware of anyone else making such lessons.
Instructions on how to create (and use) lessons can be found here:
https://www.gnu.org/software/gtypist/doc/#Script-file-commands
However, currently, there is a limitation gtypist has with lessons
that have characters with different lengths than the latin characters.
The workaround would be to reset the lessons when you make a mistake.
You can give it a try and see if it works for you.
Thank you,
Mihai Gătejescu