@NIKHIL KUMAR Thanks for reaching out.
To access an Azure key vault with your managed identity, you have to create an access policy for that identity on your key vault and assign the appropriate permissions for that identity on that key vault. To automate this either you can leverage the ARM template i.e. you need to give identity access to resources when the resource is deployed. Alternative you can leverage the Azure PowerShell or CLI to perform this manual operation. For more details, please refer to this document.
Azure Resource Manager template (ARM template) Key Vault access policy resource definition
Azure PowerShell Assign a Key Vault access policy
Azure CLI Assign a Key Vault access policy