There are two main ways to say “you’re welcome” in Chinese, depending on the regional habits.
不客气 (bu2 ke4 qi4):
This literally means “don’t be polite”, and is used in many cases. Chinese culture tends to prefer formality and politeness as a default, so telling someone not to regard those politeness norms is a ways to make them feel welcome. In some places, such as Taiwan, this phrase is used almost exclusively as a response to “thank you”
没事 (mei2 shi4):
This literally means “There is no worry”, or “no worries”. While this does not literally mean “you’re welcome”, it means that helping you was not a problem, or “it was nothing”. This is usually more casual, but can be used in formal situations in places such as Beijing.
