How can I transfer MP3 files from MacBook mini to Air?

So I have owned Mp3 music files on Macbook Mini. I want to move these to Macbook Air and I use these songs with Reckordbox app. After a lot of false dawns over the weekend with various requests from support, I have now moved these files via airdrop and all the songs are now showing on my Macbook. However they are not downloaded through Applemusic, and I have cancelled the subscription in the hope the stored offline files will move across. At the moment I cannot open these files va playlists on Apple Music and they just show as a long list on my downloaded iteme on downloads.

Is there a way to gets these to display properly in Apple music and on Reckordbox, or do I have to give up and find another MP3 itunes type app to sort this out?

[Re-Titled by Moderator]