Below are some of the options for Data Masking in Salesforce
Option 1. Use Salesforce Data Mask(Recommended process for easy and fast data masking) –
https://trailhead.salesforce.com/en/content/learn/modules/salesforce-data-mask
Option 2. We can manually use Data Loader tool to update sensitive information(time consuming process).
Option 3. We can also make use of tools like CommVault, AutoRabit DataloaderPro, OwnBackup, etc.