On TESU website : 30-day free trial at Study.com.

[ECH90]

I clicked to go to my dashboard.  The page defaults to the three boxes with the three subscription options.  If I remember correctly, I scrolled to underneath these boxes and there was an option to enter a school code.  That is the option I used to enter the code and it sent me back to the dashboard all renewed under the TESU subscription.

don't think it worked for me under exams its asking me to pay to "activate my account" but I have access to my classes again...