How can I merge Live Photos after exporting?

I exported a good amount of photos onto an external drive, to transfer them to another device. I found out that when exporting a Live Photo, it will export as a jpeg/heic, and a mov file. I saw on this forum that photos will merge the files back together, creating a live photo again. However, I've found that it doesn't merge all files back together, leaving some as back into Live Photos, and others two separate files in the app itself. is there anything I can do to get these files that won't merge together to do so? I can give more detail, if needed.

[Re-Titled by Moderator]