Unfortunately, the President has no role in the scheduling of substances. The Supreme Court has already made it clear the president cannot do this by executive order, and Congress gave the power to schedule dugs to the DEA.
The DEA takes the recommendation from HHS. HHS basically then hands the reigns over to the FDA, who then evaluates the drug, and provides evidence to the HHS based on testing and scientific research. HHS then takes that information and creates a scheduling recommendation for the DEA.
Then, the DEA takes that recommendation, does its own research and has a public comment period, and THEN it can reschedule a drug.
Since Congress gave the president no direct role in this process, all the administration can do is appoint officials they think will be supportive of their decisions, and then make their opinions known, and act as a bit of grease to get things moving.
Descheduling is even more difficult - first because of international treaties, and second - part of the reason marijuana has not been rescheduled already is due to a lack of scientific evidence for specific things the FDA looks for. This is largely because people can't do research because of its classification... So it's a catch-22.
If the DEA rewchediles weed, this would allow for further research to be conducted which in time could allow it to be fully rescheduled.
The DEA has already signalled they are planning or at least wanting to reschedule weed to allow for further testing.
See here
OR... Congress could pass a law removing marijuana from the controlled substances act.
