Unable to join breakout room

@DeFrancoM If the option was selected for these users to self-select a breakout room, they would need to click on the Breakout rooms icon. 
If for some reason they hit later on the pop-up by mistake, they can also hit the icon to join the assigned room. 

In either case, they should be able to click on the breakout rooms icon to get to the needed room. 
I would suggest having this guide below handy to provide to anyone having issues as it covers all scenarios. 
https://support.zoom.us/hc/en-us/articles/115005769646-Participating-in-breakout-rooms

If this answer helped solve your question/issue, please hit the "Accept as Solution" button below.