While this has been raised as an improvement, Add back "Change Community" on mobile 3, the ability to swap between different communities is not available in the current offering. That being said, I would recommend voting on that idea in order to help raise awareness of this request with our Product Management team.
Thank you for bringing that to my attention Jesse Fuller. I noticed there is a feature to 'bridge' communities which I found out is in place for the internal & external communities that my company uses. I haven't tested it but this may be a temporary solution to my problem however the bridge is not set up for the Jive community so I may have to ask my community manager to bridge this community as well.