How I connect to the microphone on my phone while on a desktop meeting

Hello, 

My Zoom app on my mobile phone (iOS) and my Zoom app on my computer were linked, allowing me to switch to the microphone on the phone when I was in a meeting on desktop, so I didn't have to use the built-in mic on the computer. But I disconnected that during a meeting and now I can't find the way to link them again - the option to switch to the microphone on the phone doesn't show up anymore.

How can I set it up again?

Thanks