It's not immediate. There's a process involved in rescheduling or descheduling. Biden started the process to move it to schedule 3 in 2022 which would efficiently make it legal medically. The DEA has been dragging it out as much as possible. There's a public comment period in December
Biden has also not publicly said he wants full legalization, so convincing him to do so may be difficult. As senator, harris pushed for full legalization, so it's clear that she has a very different attitude about it to Biden