In your Canvas course, click on the Assignments link in the Navigation bar.
Create a new assignment, by clicking on the + Assignment button in the upper right hand corner of the page.
Give your assignment an Assignment Name.
Add how many points you would like to award for the grade and select the Assignment Group and Display Grade as you would like for your course.
In Submission Type, select External Tool.
In the Enter or find an External Tool URL text window, paste the LTI link found in the GrassBlade editing page noted above. You can also check the Load This Tool In a New Tab checkbox if you would like the module to load in a new tab. Keep it unchecked if you want to load it while keeping the Canvas course navigation menu:
Add the Due, Available from, and Until dates if you'd like to use them.
Click Save & Publish if you want to make it immediately available to your students or click Save if you plan on making further edits to it in the future. Just remember to publish it once you're ready for your students to use it.