That’s a very easy one for them to do, as well: the subsidies were expanded dramatically by the American Rescue Plan Act, championed by Biden, and passed into law in 2021. The ARPA expanded the number of people who qualified for some level of subsidy (which is based on income level), as well as increased the amount of subsidies that lower-income Americans (who had been qualifying for subsidies previously) would receive.
Simply by not extending that portion of the ARPA, they’d roll all of that back. Or, of course, they could just kill the subsidy system entirely.