The unwritten advice is that without shell access, you depend on your web hosting provider to integrate Let’s Encrypt for you.
For example, with cPanel and Plesk (the most popular web hosting panels), this is usually automatically included.
If Alfahosting does not integrate free/automated SSL like Let’s Encrypt into its shared webhosting service, there’s not a lot you can do other than manually issuing the certificates or changing web hosts.
There’s a mega-thread of hosts that support Let’s Encrypt here: Web Hosting who support Let’s Encrypt
Manually issuing the certificates is possible via sites like zerossl.com or gethttpsforfree.com , but they are not the “proper” way to use Let’s Encrypt, because it is not automated, resulting in you having to repeat the process every 60-90 days.