I have two different numbers for both boxes 18 and 19, how do I enter this?

You can only make one entry for each box under a single locality name (Box 20).

Box 18 represents the wages for the locality, and Box 19 is the local income tax paid/withheld for that locality, so you would enter both numbers, just as you would enter both Box 16 and Box 17 for State wages and tax withheld.

The entry in W-2, Box 20, is the name of the locality responsible for assessing your local income tax. It could be a city, town, school district, or something else. Depending on where you live, you may even have more than one. If you do, just add a new row to enter info for another locality.

There should only be one Box 20 entry per locality. All of the wages taxed by one locality on one W-2 should be on a single line.