Revaluation means giving something a new value. Imagine you have some toy cars that you play with, and you think one of them is worth more than the others because it looks special. You might revalue that special car and say it's worth more than the other cars.
In real life, sometimes countries have their money revalued, which means the government changes how much the money is worth compared to other countries' money. This can happen for different reasons, maybe because the country's economy is doing really well, or maybe because they want their money to be worth more when trading with other countries.
When a country's money is revalued it can mean good things, like people can buy more from other countries with the new, stronger money. But it can also mean bad things, like if your country is really good at making things that other countries want to buy, but now your country's money is worth more, it might be harder for people in other countries to afford those things.
But overall, revaluation means giving something a new, different value.