It depends on how your data is organized. The simplest variant for only two months - you may generated help range with numbers from 1 to 31. Select Data for the chart, assign that range as X axis, after that add series with values for first month and second month. That is assumed you have values for each date of each month.
If not, to helper range with numbers you may add another couple of columns, INDEX/MATCH values into them for each month and build the graph on the top.