https://www.mydomain.com is working for me, it’s just a Comodo certificate instead.

i mean my domain: uigram.com is working but www.uigram.com is not working :)

Hello everyone,
I have the same problem but I have no idea why the solution is removed from here.
I could manage use letsencrypt to have https on my domain but when I use www.mydomain.com it redirects it to https://www.mydomain.com and the browser shows “Your connection is not private”
I am not professional in this subject so please give the response in a simple instructions.
Thanks :)