This year, because Erev Pesach is on Shabbat, the completion of the burning (done on Friday, after a search on Thursday night), is the second (slightly expanded) recitation of the Kol Chamira on Shabbat morning. The initial recitation, after the search declares the remaining Chameitz hefker, ownerless, but this cannot be a complete renunciation as one is still allowed to own and even eat Chameitz until the morning of Erev Pesach.
According to many opinions that I read here, it is permissible to make an item hefker/ownerless on Shabbat, so the fuller renunciation would not present a problem. But one opinion on the linked page reads
How, then, would someone following this opinion complete the nullification of Chameitz in a year when the first Seder is Saturday night, while still eating Chameitz for the meals on Shabbat?