Let the current bidder know and ask them if they would like to withdraw their bid.
Then, if they agree, you can cancel their bid, end the listing and relist with the correct size. (And without the pointless AI description!)
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)