How to build waves with just warriors

How do you build a defensive wave with just warriors? I have come against these waves but cannot build them myself.I use the random generator to get as many as I can and then I try to pick more using the yellow “+” but it never works. 



Just tried it Sarney? Click on each defender til youve got none then + in warriors?

@Jopman your suggestion worked like a charm. Thank you!

No probs buddy