Clavamox is usually prescibed for a cat with a cold.
It is an antibiotic, and although they cannot cure a virus, they can prevent secondary infections, such as in the lungs.
Basically the cold must run it's course, just like in humans, but the clavamox is an insurance policy.

All of mine had it. They will get over it.

Humidfiers, or shut up in a shower for 15 minutes (stay with them, don't leave them unmonitored)

L -Lysine

Hydration