To change the string as data
Right click the dimension and change the data type to Date
You could combine using graphs using dual axis concept in Tableau
I was able to change the data type to "Date", but then the chart did not display right, even with MONTH shown in the column. The line chart (Chart 2) only displays correctly when the month dimension is set to string. Thank you for your response!
Thank you for the link. I viewed your linked article and I failed to mention that I have also watched the Tableau video that discusses the topic of correcting date fields that Tableau interprets as strings. However, both, your linked article and the associated video, assumes that there are other values (day or year) contained in the string. As you can see, my months do not contain day or year values, so I have no knowledge of how to make Tableau interpret my month dimension as a date without an included day or year value.