How to change data source file of one column without changing for the rest of the columns

Hi! I have a file that I want to be linked to 12 different files - I have a table of 12 months and each month (column) should be linked to 12 different files which are in 12 different locations. I have crated the needed links in the first month (column) and I want to to copy the formulas in the next column and change the source file for it. However when I change the data source file for the second column, the data source file for the first one is automatically changed which is not my aim. How can I change it without affecting the other links? Thanks for your replies!