To start using the sensitive information permission you'll need to activate it for your account. If you are an admin with the team management permission you can activate the sensitive information permission.
Activating the sensitive information permission
At the bottom of the sidebar, click Settings
Next, click Sensitive information, displayed under "Company"
From there, click the button Activate sensitive information
You'll now see a list of all team members who are an admin. You can invite other team members by clicking the blue button Add team members
If you want to remove team members from the list, simply click the small x next to the name of the team member
If you'd like to know how to use the sensitive information in the comments, check out this article.