1) You edit that in the "My Info" section....where you edit your name and SSN. For the state of residency in there, the state selection is a list, and Texas is in there.
2) In the Other State Income at the bottom of the My Info page...TX is not in that list because TX doesn't have an income tax...but you shouldn't be entering TX there anyhow if your resident state is TX..you need to enter that up in #1.
Not sure what device you are using...but PLEASE do not prepare your taxes on a phone or narrow screen device...go to a full MAC or Windows computer...or a wide-screen tablet to continue working on it. Large screens allow you to navigate easier, and to see far more than any phone can. Taxes are too important to be messing up due to the limited view capabilities on a phone.