As per https://learn.microsoft.com/en-us/azure/cosmos-db/online-backup-and-restore
Cosmos DB backups are completely managed by the platform. Actions like restore, update backup retention or redundancy change are controlled via permission model managed by database account administrator. Cosmos DB backups are not exposed to any human actors, customers or any other module for listing, deletion, or disabling of backups. The backups are encrypted and stored in storage accounts secured by rotating certificate-based access. These backups are only accessed by restore module to restore specific backup nondestructively when a customer initiates a restore. These actions are logged and audited regularly.
When using continuous backups, you can restore to any point of time within either 7 or 30 days either into new account or existing account. With periodic backup mode, backup is taken at a periodic interval and the data is restored by creating a request with the support team.
If you came up with your own backup method, then you would need to use tools like Azure Data Factory or Azure Cosmos DB Data Migration Tool to import data back
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hth
Marcin