Yes, "once" works.
Student or Learner
"I am fond of playing video games. When I was in second standard I had a tv video game. So one day when I was in the school I thought I would play video game once I reached home" is it correct? espacially the last part. I want to say it with "Once". I know I can write "After reaching home" as well.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.