Anybody know how I can display the Airplay button on iTunes, it has just disappeared.

Hello,

New to this so sorry for the dumb question !

I had an Airplay button displayed on iTunes, but it has just disappeared.

It was showing multiple devices and I accidentally clicked on single. The Airplay button just completely disappeared, and I can't find anything in "help".

Itunes is on iMac 21.5", Late 2009, running OS X Yosemite V.10.10.3

Many thanks.