To check in your team, first make sure you are logged in at the bottom left, then click on the check in banner that appears at the top of http://tournaments.nse.gg.
If you are on a mobile device, you can log in by clicking the three lines in the top left corner to bring the side bar up.
Anyone on your team can check in and submit scores, but only one person needs to.
If you are having any issues, put a message in #admin-support for the game you need help with in our discord.