When a blog is first created in Reflect it is simply 'a blog'. Any blog can be turned into Class blog by switching on the 'Class blog' setting. If you have an Admin role or sufficient editing permissions on a blog, you can follow these instructions to convert your blog into a Class blog:

Login to Reflect (visit: https://reflect.ucl.ac.uk).
Select the blog you want to turn into a Class Blog from the My Sites drop down menu.
Click on My Class and select Create a Class.
Click in the checkbox adjacent to: Class Blog: This is a class blog.
Checkout the other settings – particularly those concerning privacy and set them accordingly.
At the bottom of the screen click on Save.