If (like me) you bought a steam deck right before the announcement of the OLED version and the price drop for the original, you can contact steam support, tell them that if you knew about the coming price drop you would have waited, and request a refund for the price difference.

I paid £369 for a refurbed 256gb steam deck, then they lowered the price to £279, and I just got £90 refunded to my steam wallet this morning after contacting them yesterday.