Thanks for asking question! If I have understood right, you have purchased certificate from Azure Services,
And have imported certificate to your Azure Key vault via certificate configuration.
If you have turn on automatic renewal of your certificate by selecting the certificate in the App Service Certificates page, then click Auto Renew Settings in the left navigation.
Select On and click Save.
Certificates can start automatically renewing 60 days before expiration if you have the automatic renewal turned on.
Renew App Service certificate automatically. Once the renew operation is complete, click Sync. The sync operation automatically updates the hostname bindings for the certificate in App Service without causing any downtime to your apps.
Additional information: As mentioned in this blog
Q. My SSL certificate is not being auto-renewed ?
Ans: All App Service certificates issued prior to March 31st 2017 will receive an email to re-verify their domain at the time of renewal even if the auto-renewal is enabled for your certificate.This is a result of change in GoDaddy policy. Please check your email and complete this one-time domain verification to continue to auto-renew the SSL certificate. Also , note that GoDaddy does require you to verify your domain once every three years and you will receive a email once every three years to verify your domain.
Hope this helps. Let us know if further query or issue remains.