Hey, im chloe and I decided to make a small how-to and saved files.

putting the save in your directory:

your directory should look like this: "C:\Users\(your username)\Documents\My Games\Borderlands 2\WillowGame\SaveData\(big number)
(your may be a different drive, C:, D:, E:, etc. but if you only use one drive it should be C:)

making the save not delete any of your current saves: 

make sure you rename the save to something following this format "save0000.sav" but make sure you change the "0000" to a set of four numbers not already in your directory, they can be any 4 numbers.

to put the file in your directory: 

unzip the folder using 7zip (https://www.7-zip.org) or winrar (https://www.win-rar.com/start.html?&L=0) and place the relevant file in your directory.