When you apply a Full Disk Encryption policy to a device, you have the option to encrypt all local fixed volumes or specify the volumes that will be encrypted. Once the policy is applied, the specified volumes are encrypted.
If you add a new disk drive to the device, or you want to specify another volume on the device for encryption, the policy must be removed, including disk decryption, and then be reapplied to recognize the new volumes. If the existing policy is not set to encrypt all local fixed volumes, you need to edit the Local Fixed Volumes setting in the policy to recognize the new volumes before reapplying the policy and encrypting the drives.