if I have a baron and a hidden blade that is hidden in battlefield a and then in battlefield b I have illaoi and a tideturner hidden. then the enemy plays a spell and I react and swap locations of baron and tide turner. does hidden blade in battlefield a stay hidden or does it go away. and also does it create a new contest in middle

No — the Hidden Blade stays hidden, and no new contest is created.

Your Hidden Blade at battlefield A remains facedown. The hidden state lasts "for as long as you control that battlefield" (Rule 811.1.b), and the swap doesn't change that: Tideturner ends up at battlefield A as your unit, so you still control it. Hidden cards are only trashed in Cleanup when they're at a battlefield you no longer control (Rule 323.7) — since Tideturner is there, that never happens.

As for the contest: Contested is only applied when a unit you control enters a battlefield you don't control (Rule 450). Both battlefields stay yours — battlefield A has your Tideturner, battlefield B has your Illaoi and Baron — so neither side of the swap creates Contested, and no Showdown or Combat gets staged by the move itself. The only thing that changed is which of your units is where; your Hidden Blade is untouched either way.