Your Google Workspace email plan can be easily renewed at any time by opening the Emails section, selecting Manage:
And clicking Renew service:
That’s it, now you know how to renew your Google Workspace 😊
NOTES:
If the email plan is past the expiration date, you can purchase a new order
If you want to add a mailbox to your account, check this article: How to purchase additional mailboxes on Google Workspace