How to create a small surface region in CREO so it can be used as a surface to apply BC in ANSYS?

I was trying to create an isolated small surface "region" in a big surface like the small rectangular surface patch on the above enclosure. I am going to export its step file into ANSYS then mesh the small patch and name it as "leak inlet", so that it can be used in CFD simulation as an inlet BC. However, there is no document or instructions on how to do it.
My real "enclosure" is very complicated. I failed to export its step file into SpaceClaimer or ModelDesigner, therefore "imprint" is not available. If the small surface region can be created in CREO (just like in Simulate) then export to ANSYS mesh tool, everything becomes easy.
Is there anyway to create this small surface region in CREO?
Thanks.

