Here's a way that I found.
First Download ZArchiver and the Mod of your choice. (Make sure first the is compatible to the current version.)
Open ZArchiver and go to MGD's data files. (Android>data>monstergirldreams.program>files)
In that folder create a new folder and name it as "game". (Without the quotation marks.)
In the New "game" folder create a new one and name it as "Mods". (Without the quotation marks. )
You can decompress/unzip/transfer the mod files you downloaded in the new "Mods" folder.
*You can turn off the mod by renaming the folder and adding an underscore before the name.
i.e. Waifupocalypse (Turned On)
_Waifupocalypse (Turned Off)
*This way shows me errors if I turn on the images setting for the game. It can be solved just by turning off the images setting.
*Check the wiki of MGD to make sure which mods are compatible.
*Make sure to make a backup save before you use mods. (Make two saves if you have to. I haven't ruined my game yet but better safe than pissed off at me for not reading this part.)
Yeet, have a good day.