Did you buy the Domain from Azure or from another vendor? -
If you purchased it from Azure, you have to enable the auto-renewal option to get it renewed automatically. in this case, most probably the auto renewal option is disabled and you may refer to the following link to see how you can renew it. Ensure you enable the auto-renew option.
https://learn.microsoft.com/en-us/azure/app-service/manage-custom-dns-buy-domain#renew-the-domain
If you purchased the domain from a third party, then you need to renew from the third party, the process varies from registrar to registrar, however, it must be a simple process, also ensure you enable auto-renew with your registrar.
Hope this helps.