The phrase was first used in songs by artists such as The Beatles and shortly after by Simon & Garfunkel. This phrase has absolutley no definitive meaning given by dictionaries or artists such as John Lennon who first used it. The phrase has two other widely known spellings: goo goo g'joob and kukukachu. It is believed to be used in songs and in 60s and 70s slang as a phrase left to be freely interpreted by anyone based on the surrounding context it is used in. The freedom to betsow any meaning upon the phrase makes the word a statement about freedom of expression, which is a meaning in itself.
Another widely accepted variation of the meaning is a slang way to assure the state of things is entirely fine; an expression of reassuring goodness. Also used as a way to introduce an effect or say "hey whatdya know--".
In "That '70s Show", Donna Pinciotti said coo coo ca choo as an end to a random string of rhymes while stoned.
Coo coo ca choo was also used by Crush the turtle in "Finding Nemo".

The time between Christ’s birth and the beginning of the coronavirus.

An expression of great exitement, or emotion.

coo coo ca choo mean's everything is alright okay and just go with the flow because you got scroll buttons like the day is long.

The phrase uttered when a cougar bags her prey.

A term used often in the hippie era of the '60s, implying that everything is fine, or that there is no need to worry about anything.

meaning that everything is fine or just dandy; or used in a situation to agree or to confirm something.