I had TurboTax import my credit card history from 2016, so that I can identify which expenses went to my 1099 job. However, I had many different 1099 jobs and am not sure how to identify which expenses from my credit card were for each specific business.

You can only use the import function for one business.  So, it is best to use the import function for the business that has the most expenses.  You will need to unclick or delete any expenses that you imported that do not relate to the business you choose to use with the import option and then manually enter the expenses for the other businesses.