Demon invasion.

I need the demons to be only 2nd tier in the army.

I still don't understand what to do after I talked to Khabeleth in the second mission and he told me to find a way out, where should I go? I couldn't figure out how to get to the portal where the succubi are. You said I need 2nd tier creatures, but I only had 2nd tier creatures except for the devils, and I couldn't find any 2nd tier devils. Then I tried deleting the entire army and going through with only 1st tier creatures, but that doesn't work either. I'm completely confused about what to do.