This could be a messy project so it’s recommended that you wear gloves, protect flooring by covering it with old rags or towels, newspaper, paper towels etc and keep a garbage bin nearby. 

You want the plunger to be covered by water, but not to the point of overflowing when you start plunging. Make a good guesstimate. If the water is going to overflow when you start plunging, use a small container to remove some of the water. If there’s not enough water in the toilet, add some so that you can submerge the plunger.

Insert a flange plunger into the toilet bowl at a 45-degree angle and position the flange in the hole at the bottom of the toilet to form a tight seal. 

With the handle sticking straight up, gently thrust the plunger and turn it to a 90-degree position.

Push downward with a gentle thrust until you see the water level in the bowl goes down. 

Remove the plunger. If the water recedes, the clog has been cleared. If a non-flushable object has been dislodged, remove it and flush the toilet.