Last Caress ( Reaction. The next unit you play this turn can be played to any battefield.) and a hidden Here to help interaction. Can I play the unit to an open or contested battlefield like last caress says I can if I use my hidden here to help before or after casting last caress?

No — the order doesn't matter. The unit still has to be played to the battlefield where Here to Help was hidden.

When a hidden card's play effect makes you play a unit, Rule 811.1.d.3 requires that unit be played at that battlefield ("you must choose to play that unit at that battlefield"). Last Caress grants a permission ("can be played to any battlefield"), and a permission can't override a mandatory location requirement — same logic as the ruling that a unit's own "play me to an open battlefield" ability is forfeited when you play it through Here to Help (FAQ #3497). So an open or contested battlefield elsewhere isn't available, whether you cast Last Caress before or after revealing Here to Help.

What still works: if the battlefield you hid Here to Help at is itself contested (opponent moved in, you keep control through the showdown), you can play the unit there — but that's just Here to Help doing its normal thing, not Last Caress. Last Caress also isn't wasted; it applies to the next unit you play normally, which is the only way to reach a different open/contested battlefield.

Note: even a non-hidden Here to Help ("to a battlefield you control") is treated as a mandatory location restriction, so Last Caress doesn't widen that either — if you want a unit to land on any battlefield, you need an effect that says so on its own face, like Thrill of the Hunt.

Last Caress isn't in my card database, so this is based on the text you quoted; no official FAQ exists for this specific interaction — the call rests on Rule 811.1.d.3 and restriction-over-permission (Rule 054).