Here are some possibilities for what you might have meant:
* Undercharge: This is the most likely meaning. It means to charge someone less than the correct amount. For example, a cashier might undercharge a customer for their groceries.
* Underchange: This is a potential misspelling of "undercharge."
* Underchange as a specific term: It's possible that this word has a specialized meaning in a particular field or industry. Can you provide any context about where you encountered this word?
If you could provide more information about the context, I might be able to give you a more specific answer.