Here to help used as a reaction from hidden, can you play your chosen champion with it?

No, you cannot use Here to Help to play your Chosen Champion from the Champion Zone.

According to the card text, Here to Help allows you to "play a unit from hand." The Champion Zone and your hand are distinct, separate zones. Therefore, a card that specifically references your hand cannot target or access a card located in your Champion Zone.

Summary of the interaction:

1. Zone Restriction: Here to Help explicitly requires the unit to be played from your hand.
2. Zone Distinction: The Champion Zone is not considered your hand.
3. Result: Because your Chosen Champion is in the Champion Zone, it is not a legal target for the effect of Here to Help.

Note: While you can hide your Chosen Champion from the Champion Zone, once it is hidden, it is no longer in the Champion Zone; however, it is also not in your hand, so it still does not satisfy the "from hand" requirement of Here to Help.

Note: I could not fully verify this ruling against the retrieved rules.