To add a diagram into an assessment form, in order to annotate it, simply follow the steps below:

Open the form builder by going into Settings, clicking the Assessments tab then click the green Create New Assessment Form button at the bottom of the page

Select the layout of your form

Click Add New Field + and select Annotation

Give your field a name then click the Choose Image (Max 4MB) button and select the image you'd like to upload

Click Finish Editing

Add any additional fields

When you're happy with your assessment click Publish & Exit