Sounds like your certificate expired. They do this every 90 days. I’m not sure what you’re asking here - there’s definitely not enough information for anyone to even start trying to help you.
How did you generate the certificate in the first place? There are, quite literally, dozens of ways to do so. The most common is using the Certbot application, in which case it’s typically something along the lines of ‘./certbot-auto renew’, but even that can change.
In that case, it sounds like it would probably be easiest to just start over. I’m going to make some common assumptions since there’s not a whole lot of info to go on here that you’re running a Linux or Unix-like OS to which you have shell access. In that case, I would recommend starting with https://certbot.eff.org/ and following instructions provided after filling in the dropdowns.
Alternatively, you can use a manual service such as https://zerossl.com/ if you’re unable to use an automated client. Note that this will require you to manually renew your certificate at least every 90 days (preferably sooner, to reduce the likelihood of service disruption in case you run into issues.)