is there a way to use yield WaitforSeconds if update function ?

is there a way to use the “yield WaitforSeconds” in update fucntion ??
or i must use that in another function

No: yield WaitForSeconds can only pause coroutines, and Update can’t be a coroutine. A smart alternative is to create your own coroutine-based Update - take a look at the CoUpdate article from @Statement. It’s basically an infinite loop that yields to the coroutine CoUpdate: this coroutine is called every frame, but the loop can only go to the next iteration when CoUpdate returns.

NOTE: Be careful when using coroutines: always save your project before running any test, because a missing yield may cause a conventional infinite loop and freeze your Unity to death - closing and reopening it is the only solution, thus all your work may be lost!

No, because Update cannot be coroutine. Maybe if you wrote more about your requirements, we could find a solution.