There was an EO, but that is not law. Cannabis is still schedule I last I checked. The order is to make it schedule III.
As far as I understand, the Schedule of Cannabis is written into the US Code. So Congress would need to amend it.
https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim...
> The term "list I chemical" means a chemical specified by regulation of the Attorney General ... until otherwise specified by regulation of the Attorney General