Kunming immigrated to Los Angeles.

This question is a bit complicated. Let's do it one by one.

First of all, let me confirm: according to the information you provided, your situation is to book a connecting ticket separately. If the whole trip is divided into three sections, you have already bought tickets for the middle section (the international section starts and ends in Los Angeles), and now you want to buy tickets for the first and second sections in the United States, right?

If it is not a cooperative airline, you can't get all boarding passes at an airport, so you may need to transfer from Los Angeles. Although, as a rule, airlines only need a turnaround? No problem, but there are companies in America that can't wait until the end. You must call to confirm. Even so, don't worry too much, because when we get to the airport, there will always be staff to complete the whole procedure for us, just walk a little more.

It should be noted that in either case, the flight number and ticket number of the next voyage need to be provided, not just the reservation number.

It is suggested that China Southern Airlines take international routes and leave the waiting time in Los Angeles to avoid the trouble of domestic flights being delayed and missing international flights.

I often have to fly. I know your hard work and anxiety. Keep asking questions and I'll help you until it's solved.