How do you edit multiple tracks for one song?

I have a song that is divided into 9 separate tracks/clips. I need to slow the tempo down. I’m new at this, so my question is this…I know how to change the tempo on all 9 tracks and then export, but when it plays back, there is a slight break between each track. What do I need to do to have the 9 tracks play seamlessly like they do on the original version?
Thanks in advance !!!

If you mean there are breaks on a CD you burnt, burn with disk at once with no two-second gap between tracks, or export and burn one file then create the tracks using a Cue Sheet: .

If you mean you are playing the files in a software player, use a gapless player like iTunes.