A continuous axis in Tableau will default to include 0 and will adjust automatically the range based on the minimum and maximum values in the visualization. However, changing the axis range can be done easily by right-clicking on the axis and selecting edit axis:
After selecting Edit Axis, you’ll see this menu with numerous options including the option to change the axis range.
For example, I can keep the start at 0 but increase the top of the range:
This won’t work if you’re using a discrete field (shown with a blue pill) for the axis. Discrete fields don’t actually create axes, they create headers. Each unique value of the discrete field will create a separate header. In the example below, since the State is discrete I don’t get the option to Edit Axis.