Half-fill the toilet bowl
First of all you need to fill half of the toilet bowl. In case it is empty then fill it half with help from a bucket. In case the toilet bowl is full and about to overflow then you need to take out some water. Use a cup to take out water from the toilet bowl until it is half filled. You need to take out the water and anything else into the bucket.
Next you need to apply the plunger in the toilet hole. You need to put the rim of the plunger firmly into the drainage hole of the toilet. Remember that it should be firmly connected all the way around in order to work the plunger properly.
After inserting the plunger, apply it by compelling it up and down. Do this for around half a minute. In the end you will hear a whooshing when the water will out of the whole. If you hear the water is still moving then insert the plunger again. Flush the toilet and if you see bubbles again then proceed to the next round.
Use closet auger
You should use a closet or toilet auger in order to clear the stubborn clog. Guide the tube down the hole and turn the crank until it gets tight in one direction. Tighten it in the other direction by turning it on the other side. Crank it in the centre and pull the tube out. Flush the toilet and in case it bubbles again, repeat the previous steps.
Use adjustable wrench
In case it still clogs, then you need to turn the water valve towards toilet off. Drain off the water inside the toilet and use an adjustable wrench to unbolt the toilet from the floor. Clear the clog from the plumbing after turning over the toilet. Then clear the drain with rubber gloves.
Fix it back
In the end fix the toilet back and turn on the water valve before flushing it.