you should have a receipt from the last time you did it. just tell them you left and came back, they will look up your house owners name, and they will see your name there and give you a new receipt. i never fill out a new form when i do it
I went to Seoul because I have done the one in Lao at savannkhet before and from Chiang Rai it is so far away. It takes 2 days to get there two days there and then two days to come back so that's already a week. And a stone's throw away from the amount of plane ticket is to Seoul. I had some friends that I stayed with in seoul so that covered my housing but food isn't too expensive, it's a bit more than Thailand but all things considered Seoul is still a pretty cheap place to be. I will for sure never do this visa in laos again now that I know that I can do this in seoul. To me, it's worth the little extra money.