Here is a simple data set to illustrate how to set the axis labels.
First, the data is transposed from what you are showing. You do need to have the data arranged in columns, where the column contains the data for a line. You can use the Edit > Paste Special to transpose in DataGraph.
Here the data is plotted using a single Plots command and a Legend command is also added.
The Axis settings are used to change the x tick mark setting from the numerical value to a label using the column Q as the label.
I recommend checking out this YouTube video below, which explains more about the Plots command. It also shows you another option for your data, which is to have it in a long or flattened format. Then you can Pivot the data in either direction as needed.
Create Color Schemes & Multicolored Line Graphs
Note that if you have the daily data, the Pivot command has the ability to aggregate over various time increments built-in, including quarterly.
Hope this helps!