Not much to go on here, but in your customize search button, you will have the ability to add to criteria and results.  You could add a column that includes month and a column that includes year to results.  Then add your data field with a formula referencing  the month for that line, and another column with formula referencing the ‘year’ field to sum.  Not totally sure given the lack of description if that will work for you; it sounds like what you may be looking to do is actually enable subtotals by month & year rather than another column.

The analytics tool may also be more able to let you compile the data how you’re trying to.