Can someone please tell me how to copy and paste

I didn't find a way to copy and paste audio from one Premiere Rush project to another, but there are other ways that you can get the audio into another project.

If you imported the audio into your project, then go to the other project and also import the audio there.

If you recorded audio in your project, then you might try this workaround:

1. Click on the Home button
2. Click on the 3 dots below the project that contains the recorded audio and select Duplicate
3. Open the duplicated project in Premiere Rush
4. Delete other audio that may be in the project (if there's audio with a video clip, right-click on the clip and select Separate Audio and then delete that audio)
5. Go to the Share mode to export the video
6. Open the other project
7. Import the exported video that contains your audio
8. Separate the audio from the exported video and delete the video portion