Can't cough, speak, or breathe
Something is blocking their windpipe. Quick action clears the airway. Coughing strongly is good — let them cough. Silence and panic mean it's serious.
If they can speak or cough, encourage them to keep coughing. Stand close, don't slap their back yet.
Support their chest with one hand. Bend them forward at the waist so gravity helps.
Hit between the shoulder blades with the heel of your hand. Check after each blow.
Stand behind them. Fist above the belly button. Grab the fist with your other hand. Pull sharply up and in. Five thrusts.
Five back blows, five thrusts. Repeat until the object comes out or they go unconscious.
Lower them carefully to the floor. Call 108. Start CPR (chest compressions) immediately.
These are short summaries, not training. Always call 108 in a life-threatening situation. If you've been trained in first-aid, follow your training.