Anyone know how to add a new title?

I think you literally have to email Mangago yourself

the instructions for it are in the images on the "Mangago ‘How to’ Guide" listing
https://www.mangago.me/read-manga/mangago_how_to_guide/

here's the specific images with it:
https://www.mangago.me/home/album/352284/

also I suggest doing the email version since they tend to look at emails more often then the DMs on here.