Older vehicles had wheel bearings you could clean and repack with grease. Modern sealed hub assemblies are different. Here is whether you can repack a sealed wheel bearing.
Sealed bearings are not serviceable
A sealed hub bearing assembly is packed and closed at the factory and cannot be repacked - when it wears, the whole unit is replaced; see hub assembly. There is no way to add grease without destroying the seal, and that is by design.
What can be repacked
Older serviceable bearings - like the tapered roller bearings on many older front hubs and trailer axles - can be cleaned, inspected, and repacked with fresh grease on a schedule. If your vehicle has those, repacking is normal maintenance.
How to tell which you have
If the bearing is part of a bolt-on hub unit, it is sealed and non-serviceable; see pressed-in vs bolt-on. If you can pull a dust cap, cotter pin, and castle nut to remove loose bearings, it is the serviceable type.
The takeaway
For a modern sealed hub, replace the assembly when it is noisy - do not try to repack it; see driving on a bad bearing. Torque the new one to spec. Keep the brakes fresh with quality pads and hardware.