Set up the iTunes Remote app for Music on Mac
You can use the iTunes Remote app on your iPhone, iPad or iPod touch to control media libraries that are on your Mac and other computers. You can download the iTunes Remote app for free from the App Store on your iPhone or iPad.
Pair iTunes Remote with your media library
Before you can use the iTunes Remote app, you need to pair it with the media library (or libraries) you want to control. Your device and your computer must be on the same wireless network and signed in with the same Apple ID.
On your iPhone, iPad or iPod touch, open the Remote app.
Do one of the following:
If it’s your first time using iTunes Remote: Tap Connect Manually.
If it’s not your first time using iTunes Remote: Tap Settings, then tap “Add a media library.”
A 4-digit code appears.
In the Music app
on your Mac, click the Remote button 
below Devices in the sidebar, then type the 4-digit code. Music pairs the library on your computer with the iTunes Remote app on your device.
Pair iTunes Remote with your Home Sharing network
If you have Home Sharing turned on, you can set the iTunes Remote app to pair automatically with any of the media libraries on your Home Sharing network.
On your iPhone, iPad or iPod touch, open the Remote app.
Do one of the following:
If it’s your first time using iTunes Remote: Tap Use Home Sharing.
If it’s not your first time using iTunes Remote: Tap Settings, then tap to turn on Home Sharing.
Sign in with your Apple ID and password.
To disconnect (or unpair) all devices from your media library, click Forget All Remotes in Advanced preferences.
The Remote app is also available on Apple Watch. See Use Apple Watch to control music on a Mac or PC.