Take a look at this post,
How to install and implement sen2cor version 2.08 please take a look the following thread,
As I mentioned sen2cor had problem of implementing directly from SNAP, Nevertheless, you could implement it from the command shell,
Take a look at the following post,
to call sen2cor from the command line, first thing you need to add the sen2cor to your path, please have a look at the following post, How to add up sen2cor to the path,
After adding up sen2cor to your path, typing the following statement in your console
L2A_Process.bat --help
Should gives you the following result,
Also here is an example of call and implement sen2cor from the console, Navigate to the directory, where the granular is existed and then, implement L2A_ Process as below
L2A_Process ./S2A_MSIL1C_XXXXXXXXXXXXXXXXXXXXXX.SAFE -–resolution=10