If your toilet unexpectedly backs up, you may be able to salvage the situation on your own if you act quickly.
Stop More Water From Getting Into the Toilet
The first thing that you need to do is stop additional water from getting into the toilet. You don't want more water to flow into the toilet, creating an even bigger mess.
To stop the toilet from filling up more, take the lid off the tank. Once the tank is closed, close the toilet flapper. If the flapper will not stay down, place something on the stopper to keep the flapper lid down. When the flapper lid is closed, no more water will get into your tank, and the tank will eventually stop filling up with water when it is full as well.
Grab Your Plunger
Second, you need to grab your plunger. Ideally, you will have a funnel-cup plunger. A funnel-cup plunger looks like it has a little cap on the end that funnels up to the larger plunger cap, it doesn't have an open plunger cap. Whatever plunger you have on hand will do, but if possible, you should keep a funnel-cup plunger on hand.
Get Your Plunger Ready
Third, take your plunger and run it under some hot water in your shower and tub. The hot water will help make the plunger more pliable; when the rubber is really hard and stiff, it doesn't work as effectively. When the rubber is more pliable, you will get a more solid seal on the toilet bowl, which will help you get rid of the clog.
Finally, you need to make sure that you plunge correctly. Take your plunger and place it inside of the toilet bowl. You want the plunger to cover up the hole on the bottom of the toilet.
In order to correctly plunge, you need to push down and then pull back up. Keep in mind that pulling the plunger upwards is just as important as pushing it back down. Repeat this process at least three or four times. After you do this three or four times, flush the toilet and watch the water carefully. If the water starts to go down the toilet, you've gotten rid of the clog. If the water starts to build up again, close the flapper right away to prevent more water from overflowing.
If this doesn't work, give your local toilet backup services a call. Your local plumber will be able to fix your bathroom situation.