Connect a USB cable from your phone to the topmost USB jack just under the UConnect screen. When you do this the phone icon on the UConnect screen should be replaced with the Android Auto icon. Tap on Android Auto and you will get a new row of icons just above the bottom row UConnect icons. Tap the one that looks like a headphone set, twice. This will bring up a list of the apps on your phone that can play through Android Auto. Spotify should be one of them, assuming that app is on your phone.
If Android Auto doesn't appear when you connect the cable then check the phone settings: Settings->Phone->Smartphone mirroring. Make sure that this option is checked. If it still doesn't come up try and different cable.
2018 Molten Silver Pacifica Hybrid Limited purchased Nov 30, 2017.