If a player use a non champion unit as chosen champion in sealed how the remedy

No — a non-champion unit can never be your Chosen Champion, even in Sealed. Sealed only relaxes the tag rule (any Champion Unit in your domain identity qualifies, TR 602.4.a.3.a); it doesn't waive the requirement that the card actually be a Champion Unit (CR 103.2.a.2, 103.2.d.3 — signature units like Tibbers are explicitly excluded).

Remedy: The judge removes the illegal card from the Champion Zone and returns it to the main deck/pool. If the pool contains a legal Champion Unit, swap it in; if not, the player may continue with no Chosen Champion — that's legal in Sealed (TR 602.4.a.5) and they draw an extra card at the start of their first Beginning Phase (TR 602.4.a.5.b).

Penalty depends on how it was caught: if the non-champion was on the registered decklist, it's a Decklist Error [Game Loss] — correct the decklist to a legal state with minimal change (TR 703.3). If the decklist was legal and this was only a setup/presentation slip, it's a Deck Presentation Error [Warning] (restore the state), upgrading to Game Loss if the opponent catches it after hands are drawn and the state can't be cleanly restored (TR 703.4.b).