My dad is a retired firefighter and I asked him a few years ago when we had my daughter, he said good hard slaps on the back are usually best but below is what google says on the matter. It's scary stuff and I hope I never have to try it but knowing is half the battle!
Do NOT put your finger into the child’s mouth to remove the object. Your finger could push the object deeper into the child’s throat.
Call 911. This is because the airway can become fully blocked.
Encourage the child to cough until the object comes out. Don't do the Heimlich maneuver. The child's cough is better than the Heimlich maneuver.
Watch the child closely to make sure the object comes out and doesn’t shift to fully block the throat.
If a child has trouble breathing but can’t talk or make sounds and is conscious:
Do NOT put your finger into the child’s mouth to remove the object. Your finger could push the object deeper into the child’s throat.
Tell someone nearby to call 911.
Do the Heimlich maneuver (see instructions below).
Keep doing the Heimlich maneuver until the object is out of the throat.
Stop if the child becomes unconscious or stops breathing.
If a child stops breathing or is unconscious:
Tell someone nearby to call 911.
Lay the child down on his or her back on a hard, flat surface such as a table, floor, or the ground.
If you can’t see the object and the child has not started breathing, place your mouth over his or her mouth. Pinch the nose shut and puff 2 breaths into the mouth. Each breath should last 2 seconds.
Do the Heimlich maneuver with the child lying on his or her back. Kneel at her feet, place the heel of one hand in the middle of her body between the navel and ribs. Put one hand on top of the other and use gentle but firm pressure to give 6 to 10 rapid thrust upward and inward.
If the child has no pulse, this means his or her heart has stopped beating. Start CPR (see instructions below). Repeat CPR until emergency services arrives, or the child starts breathing.
https://www.saintlukeskc.org/health-library/when-child-choking-age-1-12-years