Need newby help with getting cert for my nas with my zip file

I am running two Synology nas on my home LAN. My original certificate was generatedf through synology (xxxxxxxxx.synology.me). I now have my second nas being combarderd with failed logins and nas blocking attempts. I really need to get my second nas locked down with a certificate like the first nas. Apparently Synology won't set up second cert through Let's Encrypt. So after searching and reading I'm finding out that I need to use a client to set up and then send though to files from my zip file (server.csr and server.key) to Let's Encrypt to get certificate.

I've tried importing/adding those two files on nas and I get an error. Reading more now, I believe I have to send them to Let's Encrypt and that will some how generate a certificate that I need to import onto my nas.

I could really use some direction. I'm elderly retired and actually worked in IT for many years, but that was also many years ago. I did install jellyfin in docker on my nas, so have alittle experience using coding into terminal. I'm not a experienced user and could use a little help, please. I originally had a username set up for xxxxx.synology.me, but couldn't find out where I put a new name for the second nas? I'm also feeling like I need to "install Certbot ACME client" somewhere, but the major coding it used was beyond my knowledge.

If this level or support and patience is below this site, is there somewhere else I could look for elementary assistance? Thank you in advance.

Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.

My domain is: was synology.me on first nas.

I ran this command:

It produced this output:

My web server is (include version):

The operating system my web server runs on is (include version): Linux (modified)

My hosting provider, if applicable, is:

I can login to a root shell on my machine (yes or no, or I don't know): I don't know.

I'm using a control panel to manage my site (no, or provide the name and version of the control panel):

The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot):