As @Rusty said you can reset DSM.
DSM is the operation system of the NAS, reset is a factory reset, will put the device with all factory settings.
I never done in a Synology NAS but i done that in many other devices.
Your hard drives must work after a reset, because you dont format the hdds but only a hard reset , it affects only the device.
If you are using HSR (hybrid synology raid) hdds with only work with devices that support HSR.