I have run into an issue where I don't see the sync option when I go to azure app -> tls/ssl settings -> .pfx certificate. I am updating a new version of my certificate in keyvault but in my app its not allowing me to sync. Until 4 days ago I could see that sync option don't know what went wrong meanwhile
Sync
option is enabled if the certificate is out of sync. Also, note that App Service automatically syncs your certificate within 48 hours. However, if you want to force sync, go to App Service Certificates page. Navigate to your certificate -> Go to Rekey and Sync from the left navigation -> Sync. For details, refer TLS/SSL certificate in Azure App Service.
By the way you can also check if cert is in sync by clicking the linked cert in the bottom pane.