how to make a custom keyboard for your phone

hello guys im srry but this has nothing to do with unity but i now tat this place is filled with fellow coders and stuff so i nee some help ok im trying to make my own custom keyboard for my phone its going to be filled with unqie images no letters and stuff i already made some of the images but i just need help to know where nd how i can make the keyboard and how can i download it to my p\phone by the way want to know how to do it for both android and apple devices