It seems you’ve managed to obtain cert(s) that cover the name(s) you expect to secure.
This site is here to help you get, and automatically renew, those cert(s).
[which you already figured out]
I think you now need help with using the cert(s) with the programs you want to secure.
That help would come from forums about that program or the program vendors’ site.
and if you have further trouble with that you’ll have to ask the Blogger team, or on a forum for Blogger users.
The Let’s Encrypt community can’t help with this because our services and technology don’t enter into the picture at all here, unless you plan to change your hosting away from the Blogger service and onto some other hosting provider.