Change existing Custom Field to Accounting Dimension

I created a doctype “Container” and added in Sales invoice item table as a custom field to generate sale report container wise but now I also want to generate Profit and loss report container wise. I could have achieved this by creating a accounting dimension of “Container” (at that time I didn’t know that). Is there any way change it to a Accounting Dimension? I tried to create the dimension but it doesn’t work.