The Zoom meeting capacity with Webinars

Hi , 

We have  zoom meeting account with  100 capacity, and recently purchased Webinars license, what we know the Webinars with 500 capacity, We assume that we also should have 500 capacity in the s=zoom meeting too( we need breakout room feature in the meeting).  

looks like it only allow us with 100 capacity,  is there special setting to have 500 capacity in the meeting > or we have to create the webinars first with 500 capacity and convert to meeting ? 

Thanks.

Bing