How to reset clock when battery changed on a car?

Is in the Owner's Manual.

The manual should show how to reset the clock. But if you use a keep alive circuit when removing the battery, it will retain its memory.

A keep alive circuit is a 12 volt power source hooked to the ground and a 12 volt circuit using clips, or plugged into the cigar lighter that keeps 12 volts applied so the various computers in the vehicle don't lose their memory, things like radio presets, clocks, etc.

Check your car's owner's manual if all else fails, and try pushing the buttons to see how they work. You can buy a battery that plugs into your cigarette lighter that keeps your computer and radio's memory in tact when you disconnect the main battery.

they make a memory saver that plugs in to the power port in your dash it uses a 9v battery to keep the clock and computer memory from resetting or you can look in the owners Manuel on how to reset the clock

Check your owners manual, but if not I would try pushing and holding the power button till the time flashes, that usually means its ready to be set. Then use the buttons that turn the radio stations or the cd controls fast forward or rewind and see which one make the numbers move, then which ever one does it set it and push the power button again. that usually works for me