Since you have failed to provide any useful information like a clear photo of the label or of the ends of the motor assembly where any fastenings are probably located, you are on your own mate!
Some general notes: The gearbox is normally attached with screws going into threaded holes in the faceplate of the motor. Sometime they are long through screws, sometimes you have to dismantle the gearbox to access them. Even if you succeed in removing the gearbox, its input gear is usually semi-permanently bonded to the motor shaft - either a high force press fit, or adhesively bonded, and will not be removable in reusable condition without specialist tools, and the gearbox will be unusable without a matched input gear.