To Edit the Year or Month of Multiple Files at the same time:
Click the Files page on the left-hand navigation.
Select all of the files whose Year/Month needs to be changed by clicking the checkbox next to the file name.
Scroll to the bottom and click the Tag icon.
Click Add & Remove Tags.
Click the Year or Month radio button.
Click the dropdown menu and select the desired Year or Month option.
Click Replace.
Note: you can only choose to edit one of the options at a time, meaning if you need to change the Year and Month, you first have to change the Year, then you can click on Add & Remove Tags to change the Month.