Once again, make sure you are in the Axis Options category from the left menu. Since the horizontal axis of a chart is usually just text instead of numbers, you will not have as many options as for the Y axis. (you can also select one of the default options listed from the current menu) Select your chart and then go to the Layout tab and click Axes > Primary Horizontal Axes and then More Primary Horizontal Axis Options. If you change this, you should also look down to the option Minor tick mark type: and select something other than None so the marks will appear on the chart's Y axis. This should be a value smaller than the Major unit.

Minor unit the second numeric interval and determines where little tick-marks will be placed along the Y axis. Major unit the numeric interval at which lines will be placed across the chart and at which numbers will be displayed along the Y axis. Maximum says what the maximum number on the Y axis will be this is mainly used for changing the scale/appearance of your chart. This will affect the scale of the chart so pay attention to how it looks after you change this option. Set this to 0 to start the axis at 0 or set it to any other number. Minimum is the number at which the Y axis (vertical axis) will begin. Select the Fixed option for any one of those items and you can then change them as needed. Make sure you are in the Axis Options section from the menu on the left and look to the 4 options at the top:

(you can also select one of the default options listed from the currently visible menu) Select your chart and then go to the Layout tab and click Axes > Primary Vertical Axes and then More Primary Vertical Axis Options. You can change the size of the units on a chart axis, their interval, where they start, where they finish, and more.

Excel graph axis label increments