@mde First of all, like others have hinted, preventing this ‘damage’ is easier than repairing it. Please take better precaution against dust when changing lenses. You really don’t need laboratory conditions for that. If you keep the mount pointing downwards at all time when changing lenses, gravity helps to prevent dust to settle. And if your sensor is really dirty (which it is), you might be better of to have it professionally cleaned by your local photolab.
Having said that, if your dust hasn’t moved since you took your photos, you can also use RawTherapee’s flat-field correction to get rid of the dust spots. Flat-Field - RawPedia and in particular this section Flat-Field - RawPedia
If your dust has moved, this method is useless and you should resort to the clone brush in e.g. GIMP, as RawTherapee doesn’t have a proper spot removal tool (yet). You can also read more here RT: No spot removal tool? - #18 by Hombre