Select 'Libary Donation' and the donation you want to duplicate or reuse. Select 'Donation, Duplicate Donation' from the menu. Edit the donation as needed.
Once a donation is in an auction, specific bids might be assocated with the donation. If you switch auctions for that donation, the bids are no longer in that auction. Therefore, it is better to duplicate the donation and associate the duplicate with the new auction.
However, if nobody made a bid on that donation, there is no objection to swithcing the donation from one auction to another.