Extract zip file.
In your Bloodstained Ritual of the Night install location navigate to "BloodstainedRotN\Content\Paks".
If there's no "~mods" folder, create it.
Drop "Gleem_Drop_Rate.pak" file into "~mods" folder.
Enjoy!

Note, this mod is not compatible with any other mod that altars the "PB_DT_DropRateMaster.uasset" file.