How can we change label in Approval details?

We would like to know how to change label in the Approval details page. When an employee submits a certification, he needs an approval from an HR, and when the HR goes into the Approval details page, there's a label that appears (Submitted by) that we would like to change. We tried to do this by using the "User Interface Text" page in the sandbox, but we couldn't afford to change this label. How can we do this?