To use this mod you will need to download the Red dead radio mod
Remembering that this will not replace the standard soundtrack of the game, you will only have an mp3 player within the game that you can play the songs from the rdr1 undead nightmare.
To install you need to place the files inside the mod’s Radios at: Red Dead Redemption 2 \ Red Dead Radio
When you install you just need to press Q + R to open the Radio inside the game and select the radio and soundtrack you want to use.
Credits:
RedMaxBR – with the mod of kostas96b