You have two options:
Just copy the Audio Region to the clipboard (double-tap and tap on Copy)
Open the other Song, create an Audio Recorder or Guitar Amp Track and paste the Region onto that Track (double-tap and tap on Paste)
Access on the computer
Transfer the GarageBand Project file to your Computer (via iTUnes File Transfer or iCloud) and open the Project File (ctr-click and select Show Package Content from the shortut menu). Inside the Media folder are all the Audio Files that you used on that Song, loops or newly recorded).
You can copy any audio file from that folder and use anywhere youw want.Hope that helps
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