My seized tap is for the cold water on an old bathroom sink, which is separate from the hot water tap.

If you tell us the brand and the model number of your faucet we will more than happy to help you, it may be the cartridge, the seals, Thanks.

John

My seized tap is for the cold water on an old bathroom sink, Turn the water off and unscrew the bonnet packing nut, ( The nut directly under the handle. Now back the stem assembly out counterclockwise. Lube the threads with Plumbers Heat Proof Grease and reassemble. Turn the water back on and open the fasucet a little. If the packing nut leaks a bit simply snug it up a bit until it stops,
NO NOT OVERTIGHTEN The nut. Good luck, Tom