Is transitioning to the second screen form after filling out the first an include or extend in Use Case?

Transition to the second screen form after filling out the first one is modeled as an "extend" if the second form appears optionally or depending on conditions. If the second form is a mandatory part of the process, then it is more like an "include".

In most cases, a sequential transition between screens is an include, as the second form is part of the main use case.