If you accidentally gate-check your bag and it has your passport in it, the best thing to do is approach an airline customer service representative at the gate where the plane arrived to inform them of what happened, Dan Bubb, a professor at the University of Nevada, Las Vegas and former airline pilot, tells Travel + ...

If you accidentally put your passport in your checked bag, you have a major logistical emergency that needs to be addressed immediately at the check-in counter. You cannot clear security or board an international flight without your physical passport in hand. If you realize the mistake before the bag has been sent down the conveyor belt, the agent can simply stop the process and let you retrieve it. If the bag has already "gone down the belt," it enters a massive, automated sorting system where it is nearly impossible to retrieve quickly. You will need to alert a supervisor; they may be able to intercept the bag at the security screening point or the loading tug, but this often takes 30 to 60 minutes and is not guaranteed. If the bag is already loaded onto the aircraft, the airline may refuse to retrieve it to avoid delaying the flight. In the worst-case scenario, you will be denied boarding. If this happens on an arrival (e.g., you realize your passport is in your bag while at the immigration desk), you will be held in a secure area while the airline staff attempts to locate your luggage in the arrivals hall, which can lead to hours of delays and potential questioning by border officials.