Assuming you provided an e-mail when creating your account (which probably happened if you typed in your e-mail address at all), you will receive an e-mail from the CA when the certificate is near expiry, if it hasn’t been renewed with precisely the same set of domain names.
Autorenewal is a feature in some of the Let’s Encrypt client software, but it depends on which software you used and how you used it. For creating a certificate manually on your own computer, automatic renewal is very unlikely to happen because the same proof-of-domain-control steps will need to happen again every time. If those steps were performed manually the first time, there’s no way that they can be performed automatically in the future.
Depending on your host OS, your level of access, and possibly your level of comfort with scripting on your own computer, you might be able to set something up so that automatic renewal will happen, which we’re happy to discuss on this forum. Otherwise, I expect it won’t be automatic.