...
Go into an assignment (on Canvas) that requires the use of TCI.
Take note of the assignment name (TCI: Ancient Rome - Lesson 33 in this example). 
Choose TCI Login from your Canvas coursescourse's sidebar navigation.
Choose Teach Now from the TCI landing page.
...
Open the Unit/Lesson dropdown menu. Select the Lesson Name from the assignment you need to grade. Note - The lesson # in Canvas directly relates to the numbered lesson in TCI.
Title in Canvas:
Title in TCI: 
Scroll down to the Notebook Answer Key. Select Actions > Download PDF.
Use the PDF to grade your students' screenshots in Canvas SpeedGrader.