Add drive to RAIDZ2 pool in TrueNAS SCALE

Hello everyone,

I would like to add another drive to my RAIDZ2 pool in TrueNAS SCALE. I currently have 4, 2TB drives in 1 RAIDZ2 pool and I am looking to add a fifth drive. I see the expand pool button at the bottom of the pool actions context menu, but I can't find a way to add a drive to the pool so it can be expanded.

Thanks,
Milan Mehra