How to add one texture to another (combine)

Hello for every one !

I developing a 3D game.


I have 3D Character and I want to be able add some "tattoos" to his face programmatically.

I have dae file with 3D model (from Maya) and two different textures. One for the Character skin, another for the tatto (It is a "Star" for example).

I add Character skin like a First Material and it looks like this :

https://ibb.co/fFRHmv

I want to add tatoo "star" to a skin.

https://ibb.co/bZmHmv


How can i do this ? Is it possible ? . If i add tattoo "star" texture as the second material nothing happens 😟


Thank you for the answer