What is the formal form of Como estas?
Hola, hflan, bienvenida al foro. If you click on more tab at the top of the page you will find a dropdown menu with interesting articles there. If you select reference and then technical support you can find a couple of articles that can teach you how to type the tildes (accent marks). If you look for the 2nd article on that subject you might find it very useful. Not only tildes but other characters as well, such as ñ ¡ ¿ and so on. Have fun y otra vez, bienvenida.
Written like that it doesn't have any formal version:
Como estas = like this
¿Cómo estás? = How are you? (informal)
¿Cómo está? = How are you? (formal)