Read this page to learn where to buy silicone rubber.

Put the wheels close one to another and put them all on a smooth surface. The surface will be dirty after the process so a disposable may be a good choice.

Use 2 components; mix them according to the manual. For the chemicals in the picture, the ratio is 1:1. For 4 wheels depicted here, 20 g of the mixture is enough. Other wheels may demand a different mass.

It is easy to mix the components using a scale in the picture below and a small plastic container. Put the container on the scale, turn it on, pour 10 g of one component, put the other component until the scale reads 20 g. Mix thoroughly and vigorously. A common mistake is a too short mixing, resulting in a mass that will never stop being liquid. Around 3 minutes should be enough. You shouldn't be doing it too long as will be ever harder to pour the mass.

Pour the resulting liquid into 4 wheels-molds. Be quick as it loses viscosity rather fast. Wait until it hardens completely. Some liquid will inevitably be lost, spilling near the molds.

Wait at least a couple of hours.

Remove excessive rubber with a sharp knife. Using a diagonal cutter, peel the outer curved part of the mold, exposing the rubber as a new contact area between the wheel and the surface below. Be careful not to damage the rubber.

Here is a finished wheel. Despite not a perfect look, it will stick to the surface very well, driving robot over bumpers and along a steep ramp.