Below are some of the options for Data Masking in Salesforce

1. Use Salesforce Data Mask(Recommended process for easy and fast data masking) –

https://trailhead.salesforce.com/en/content/learn/modules/salesforce-data-mask

https://www.infallibletechie.com/2020/02/salesforce-data-mask.html

2. We can manually use Data Loader tool to update sensitive information(time consuming process).

3. We can also make use of tools like CommVault, AutoRabit DataloaderPro, OwnBackup, etc.