Open the Alexa app. If you don't have it installed you can download it here.
Select Devices->Echo & Alexa
Press your device home button and open up the iOS Settings app, then select Bluetooth
Select your Alexa device from the list. The device will then announce that "it is now connected to (Your) iPad".
Once paired, you can go ahead and close both the Settings app and the Alexa app.
Once you are paired to the Alexa device you can rename it by tapping the "i" under Settings>Bluetooth and rename the device to something more memorable.
If you have connected via Bluetooth to this device before, sometimes the iPad / iPhone won't connect to it again this is an iOS Bluetooth issue
Simply tap the "i" icon next to the name and choose "Forget this device". then rescan for Bluetooth devices and now select it. It should now pair for you.
In MusicStreamer your Alexa should already be selected as the playback device. If it isn't, simply tap the AirPlay icon to the right of the volume slider and select your Alexa from the list.