The full saying, “There’s no use crying over spilled milk,” means that we shouldn’t waste time regretting something that cannot be changed. There’s nothing that can be done once the milk is spilled except clean up and move on.
Spill is a regular verb in American English and irregular in British English. In American English, the simple past tense form and past participle are both spilled. British English shares the same past tense, but the past participle is spilt.
To make sure you have the right spelling of spilt or spilled, you can use the QuillBot Grammar Checker.