That email reminder would I believe have come from your
https://my.avast.com (avast account).
Soon the avast installation would provide also renewal reminders, at that point you could use the avastUI, Maintenance, Registration/license section to renew.
Don't renew too soon and from outside the avastUI as there would be no way to link your existing license expiry with your new license period. Renewal from the avastUI, Maintenance, Registration/license section is able to do that so you don't lose any days on your existing license period.
Should that happen no drama it can be corrected y contacting sales (at) avast (dot) com.
