How do I swap out party members during the assault on Drezen?

[Zennistrad]

I'm playing on Normal difficulty and both of my Melee Fighters (Oleg and Seelah) have died thanks to those insect demons spamming constitution poison and paralysis abilities. Even after the Death's Door ailment, there's nothing I can do to revive them now, since I don't yet have Raise Dead.

I do have some good backup party members, but I can't find any way to actually reach them. The only option I can think of is restart the assault on Drezen, and that would require losing two hours of progress. What do I do?

[Soul]

find the queen or irabeth that is with you in drezen... wilcer garms is there and not sure specifically who but someone or something around them allows you to switch party members.... the locations change depending on your progress throughout the city in retaking areas I believe...

[Yannir]

Might want to slot in Delay Poison, Communal. It lasts an hour so it should last you through the whole instance.