You can enable Availability Zones by using Azure portal when creating an Azure Cosmos account.
You can enable Availability Zones by using Azure portal.
Step 1: enable the Geo-redundancy, Multi-region Writes
1. In Azure Portal search for and select Azure Cosmos DB.
2. Locate the Cosmos DB database named cosmos10543936
3. Access the properties for cosmos10543936
4. enable the Geo-redundancy, Multi-region Writes.
Location: West US region

Step 2: Add region from your database account
1. In to Azure portal, go to your Azure Cosmos account, and open the Replicate data globally menu.
2. To add regions, select the hexagons on the map with the + label that corresponds to your desired region(s). Alternatively, to add a region, select the + Add region option and choose a region from the drop-down menu.
Add: West US region

3. To save your changes, select OK.
Reference:
https://docs.microsoft.com/en-us/azure/cosmos-db/high-availability
https://docs.microsoft.com/en-us/azure/cosmos-db/how-to-manage-database-account