I have never used DPD but asked Mr. Google and these are the answers I found:
The notifications we send after collection, and on the day of delivery, include a link through which you can change the delivery date or address.
DPD will leave a card, telling you they tried to deliver. Please call the number on the card to arrange a convenient time for your order to be delivered. If you don't call DPD, they'll try to deliver your order on the next working day.
@rach19740