A level 1 wizard who throws a frostbite deals damage to 1d4 + its spell modifier.
As you have already noticed, a can trip is automatically raised to half the wizard's level and rounded up. A level 1 wizard can increase something to 0.5 * 1, rounded up. 0.5 * 1 = 1. Therefore, the Cantrip can only be cast as a level 1 spell (minimum level). As a level 1 spell, the Frostbite deals 1d4 damage plus its spell modifier.
Another way of thinking about it (but drawing the same conclusion) is that the Frostbeam is a Level 1 Cantrip. A can trip is magic. Given that the highest level spell location that your level 1 wizard has is level 1, there is no real way to increase the spell. The Cantrips page you linked to says it like this:
For a typical caster, this means that their level corresponds to the highest level of your magic slot.