Hey! Look here: https://docs.godotengine.org/en/stable/tutorials/ui/gui_using_fonts.html#bitmap-...
In short, you could add your image (I guess in any format supported by Godot: png, bmp, jpg) to your Godot project. Then select your file in Godot's file navigator and switch from Scene tab to Import. Here you can follow tutorial by changing Import type from Texture2D to Font Data. You'll find it easier if you put them together in the correct ASCII order, see the article on how to do that. Feel free to ask any questions!