Measure the baseboard and make a mark with a felt tip marker to indicate where you'll make the cut.
Attach a tile cutting kit to the base of the rotary tool. Adjust the base's depth so the bit only cuts to the thickness of the tile baseboard.
Rest the rotary tool's base on the wall so the cutting bit is slightly raised off the very top of the baseboard. Turn on the rotary tool and slowly sink the bit at the top of the baseboard until the base is flush against the tile.
Slide the rotary tool down so the cutting bit follows the cut line. Stop cutting when the tool base reaches the floor. Turn the tool off and wait for the blade to come to a complete stop. Remove the blade from the wall.
Remove the base of the kit to expose the cutting bit. Slip the bit inside the cut near the lower portion of uncut tile. Turn on the rotary tool and gently slide it down to cut the remaining tile.