You can lock a team member on your Karta account from the Team section.
In the Team table, find the member's profile you want to lock and click on it.
Open the More options dropdown list on the right side of your screen and select the Lock User option.
You will get to a confirmation page. If you are sure you selected the right member's profile, click the Yes, lock button.
Who can lock a team member?
Only Owner and Admins can lock a member. You can read more about roles and permissions in Karta here.