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. crt.sh | 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: resources.kanban.university
I ran this command: unable to login
It produced this output: no
My web server is (include version): unable to login
The operating system my web server runs on is (include version): linux
My hosting provider, if applicable, is: n/a
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): no
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): n/a
If you don't know how you got your certificate in the first place I'd suggest you start again. If you cannot login to your system (i.e. you have no administrative control) then your certificate is not the biggest problem you need to solve.
Though I have renewed the domain and SSL certificate is valid for 90 days but when I browse the url it says "Error establishing a database connection".
What would be the issue?
It's unrelated to Let's Encrypt, SSL or your certificate, but your site is returning an http 500 error, this means the server is encountering a problem when it tries to process the request. I'm guessing your site is using Wordpress as the content management system and that it's failing to connect to the database it uses. You'd need to check the wordpress database connection configuration and that your database service is actually running.