1. Make sure that your org has an active encryption key. If you’re not sure, check with your administrator.
2. From Setup, in the Quick Find box, enter PlatformEncryption, and then select EncryptionPolicy.
3. Click Encrypt Fields.
4. Click Edit.
5. Select the fields you want to encrypt.All new data entered in this field is encrypted. By default, data is encrypted using a probabilistic encryption scheme. To apply deterministic encryption to your data, select Deterministic from the Encryption Scheme list. For more information, see “How Deterministic Encryption Supports Filtering” in Salesforce Help.
6. Click Save.