Can anyone help me convert a 480 light fixture to work on 120

Are you planning on changing out the fixture and the bulb with a unit that will operate on 120?

I was hoping not to I just didn't know if there was a way to make the unit run on 120 can the transformer be stepped down to run on 120?

You can get a transformer rated 120 volt/480 volts, need to size the VA 25% higher than the input watts of lamp and ballast combination.

For example, a 400 watt metal halide fixture will have an input of 450 watts plus 25% will require a transformer rated at least 600 watts (VA).

And by the time you buy and wire the transformer you could have either replaced the ballast kit in the fixture or replaced the whole fixture itself, for less cost and less work.

It is a rare case where making a 480V HID fixture work at 120v is worth doing.

Are you sure the fixture is not multi-tap?