If DHL was used because the parcel is extra large there is not an alternative on ebay.
You could cancel with buyer's agreement (via the dropdown actions menu arrow for the item on your orders list) and relist, opting out of Simple Delivery and using your own choice of postage, for the buyer to buy again. Follow the advice on here:
https://community.ebay.co.uk/t5/Seller-Central/How-do-you-list-anything-bigger-than-61cm-Part-two/m-...
Or buy different postage yourself and change the tracking number via View Order Details > Postage > Track Package > dropdown arrow > Add Tracking on a desktop browser.
@baggls1