If one of the lots you have offered up for auction is no longer available, you can withdraw it from the auction during the review days prior to the auction starting. This is the period in which sellers can provide feedback on their lots before the auction is open for bidding.
To edit your lot or contact the expert, go to > My offered lots (from the dropdown list at the right top hand corner of the website) and click on the lot you'd like to edit. From there you can follow the steps to edit and in the 4th step, you can contact the expert if you wish.
Please note that after the lot is planned or in auction, you can no longer make any changes.