You can control the distance in two ways.
(1) Use the Axis settings, to set the Space for y. For example, you can set to ‘Narrow’ and then the space will be much less but will still scale with the font size. Here is the help documentation.
https://community.visualdatatools.com/datagraph/knowledge-base/command-main-axis/#space
Note that if you Control-click (right-click) to the left of the axis line, you can access this option (Y space) and other axis settings, directly from the graph.
(2) You can also control this distance by setting the left margin in the Canvas settings from Automatic to a value (e.g., 2cm). This will override the settings in the Axis settings.