Can someone help me? :(

there’s this trick that marcus koh does everytime, this, i think its like a boomerang but behind his left arm. cant seem to get it…

Markus koh does a lot of tricks. That’s not helpful for helping you. Video?

I know what you mean but have no idea how to do it. I’m sure if searched around you could find a tut.

Sometimes, things are exactly like they seem, so the trick he did could very well be boomerang behind his left arm. In this case, you can try watching the video again and practice it.