how to file for child support

Thanks in advance for any response.

I am a divorced father of two girls. I have been raising them on my own
for 6.5 years. My daughters are 8 and 14 years old. They live with me
full time, 365 and 24x7. They have only talked with the mother a few
times a year on the phone, but have not seen her in 6 years.

Anyway, I think it's time that I ask for child support. My question
is....Where do I start, how do I accomplish this task.

I live in Texas, at the divorce I declined any support. The judge told
me that if I ever want it (child support and health insurance) to come
back and ask for it.

I am sure its not that simple. There must be some paper work or court
papers that need filing.

Any help appreciated.

Thanks