きのぅはぃでした is this sentence correct? Why not yesterday?

You can't even say "ぃぃでした" upstairs. Go back and learn Japanese again.

The sentence "きのぅはぃぃでした" is grammatically correct, but no one says so.

There are two common sayings.

The first one is like the third floor: yesterday, the same day, the same day, the same day.

The second kind is: yesterday, the same day, the same day, the same day, the same day, the same day, the same day, the same day, the same day, the same day.