This forum is for iMovie for Mac than is a different app than iMovie for iPad. You might want to post your question on the iMovie for iOS forum. Here's the link:
iMovie for iOS - Apple Community
With iMovie for Mac you would create a duplicate project and then detach the audio from both videos, and move the audio clip from Clip No. 2 to Clip No. 1. Then delete video Clip No. 2 and the detached audio clip from Clip No. 1. After syncing up Clip No. 2's audio with video Clip No. 1, you can then export out the project to merge the audio and video into one clip. Because you were working with a duplicate project you would still have all of your original work preserved in your original master project. However, as I say, iMovie for iPad is a different app and so the procedures may not be the same.
-- Rich