Download and Save in your seqbaby_data folder located in the Data folder.
To find the required folder:
Options – Show REAPER resourse path in explorer/finder
Find Data folder and open…
Find seqbaby_data folder…
Copy _Abbey Road.txt to seqbaby_data folder
Restart Reaper – Add Sequencer Megababy to FX in a track.
Go to – Drum Map note names and choose _Abbey Road.txt
Should all be working – if you already have Reaper open you will need to restart.