Assume everything is setup correctly, there is nothing to do. You can test by doing a dry-run as follows:
sudo certbot renew --dry-run
Here is a sample output from doing a dry-run.
~$ sudo certbot renew --dry-run
Saving debug log to /var/log/letsencrypt/letsencrypt.log
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Processing /etc/letsencrypt/renewal/my-domain.com.conf
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Cert not due for renewal, but simulating renewal for dry run
Plugins selected: Authenticator nginx, Installer nginx
Renewing an existing certificate
Performing the following challenges:
tls-sni-01 challenge for my-domain.com
http-01 challenge for portal.my-domain.com
tls-sni-01 challenge for www.my-domain.com
Waiting for verification...
Cleaning up challenges
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new certificate deployed with reload of nginx server; fullchain is
/etc/letsencrypt/live/my-domain.com/fullchain.pem
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Processing /etc/letsencrypt/renewal/portal.my-domain.com.conf
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Cert not due for renewal, but simulating renewal for dry run
Plugins selected: Authenticator nginx, Installer nginx
Renewing an existing certificate
Performing the following challenges:
http-01 challenge for portal.my-domain.com
Waiting for verification...
Cleaning up challenges
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new certificate deployed with reload of nginx server; fullchain is
/etc/letsencrypt/live/portal.my-domain.com/fullchain.pem
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** DRY RUN: simulating 'certbot renew' close to cert expiry
** (The test certificates below have not been saved.)
Congratulations, all renewals succeeded. The following certs have been renewed:
/etc/letsencrypt/live/my-domain.com/fullchain.pem (success)
/etc/letsencrypt/live/portal.my-domain.com/fullchain.pem (success)
** DRY RUN: simulating 'certbot renew' close to cert expiry
** (The test certificates above have not been saved.)
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