There does seem to be a new certificate issued which is valid until November, so I would guess you would just need to install that one.
I would check what certificate is actually installed, but I can’t because the domain is currently hosted with ProFreeHost, not with us. So please check your account there and ask their support if you need help.
Or feel free to move your site here of course, if you like our community more!
You can certainly try with backup plugins. But if you want to make things easy on yourself, I would strongly suggest against wasting time with those. Backup plugins, at least on our hosting, generally don’t work due to file size and server power needed to restore a site that way.
Going the route that’s recommended both by us and by WordPress, which is to move the files and database by hand, is the method with the highest chance of success.