As the OS in the drum station is stored in ROM, there is no way to perform a factory reset without replacing the EPROM.
The Drum Station holds the factory presets and OS in ROM - ie cannot be overwritten. The Drum Station has 40 memory locations, the first 25 of which are ROM. As these cannot be overwritten, there is no factory restore.
For the Drum Station, copy the 00 program into locations 25 to 40 inc. This is a basic kit, and will effectively reset all of the memory locations.