Placement of Previous and Next button in Setup

What is the best placement of a previous and a next button for a setup kind of scene?

We have a stepper but we decided to have both a stepper and the previous and next buttons.

Is it better to place them relative to the data? (so if a user adds data, the previous and the next button moves more to the bottom)

or

to place it in a fixed space (so no matter how many data a user adds, it stays in place in a sticky way)