There’s nothing you need as far as “account recovery” goes, just start over with a new certificate like anyone else installing Let’s Encrypt for the first time would do. There’s no strict account setup here or anything - all an account does is provide a means to revoke certificates you lost the private key for, and as as way to get notifications for impending expirations on any certificates issued by that “account”. (It really just asks for an email on first issue and generates an account key for you.)
As Schoen mentioned, there are literally dozens of options for interacting with Let’s Encrypt, mostly dependent on your setup. We can’t help you without more information. Are you on Linux? Windows? Are you using Apache? Nginx? IIS? Are you able to log into your system on a command-line, or using a shared hosting control panel? Who is your hosting provider, or are you hosting yourself? All of these questions are asked when you create a post for good reason.
If nothing else, check out https://zerossl.com, which will let you issue a Let’s Encrypt certificate manually via HTTP or DNS challenges to get you started quickly. It’s totally system-agnostic, just requires that you can either A) place a specific file in the .well-known/acme-challenge path of your domain or B) add a TXT record to your domain’s DNS with specific contents. Then you’re given a certificate to do with what you please.
The “preferred” method for this community is the Certbot client, as it is the client created by Let’s Encrypt so it’s the most supported here, however there are plenty of instances where it’s not an ideal choice (not the lest of which being if you’re on Windows, since it’s Linux-only). If you’re really enterprising, you could even write your own client.