Fighting tax reassessment of commercial property

Background: Someone I know owns a commercial lot in Toronto. They have 4-5 commercial tenants and some commercial parking spots for rent.

Problem: The City of Toronto just did a reassessment. They deemed part of the land "residential", not commercial. The land in question used to have a house on it. But this was decades ago, and the house was demolished. Now they have to pay an extra 15k+ in taxes.

Any info/thoughts on filing a reconsideration?