The quantity is too large to adjust each event one by one…
What do you mean by “foldered?” It’s not a verb I’ve seen before.
Have you tried setting project’s master bus volume fader to +1 dB?
Have you considered using the Reaper batch file converter to apply a +1 db volume change to all audio files?
Otherwise, I would look into scripting in FMOD Studio.
https://fmod.com/docs/2.02/studio/scripting-terminal-reference.html
Another possible solution would be to assign all the events you want to adjust to a VCA, and apply the adjustment to the VCA.