Navigation path unclear

Hello,
I start introduction to programming yesterday.
I enjoyed several pages of lessons with the bouncing balls - changing colours and scripts.
I did not complete this series of pages / lessons.
Today, I appear unable to navigate to this page? lesson? to complete it.
I am now directed to https://www.codecademy.com/paths/code-foundations/tracks/cf-introduction/modules/introduction-to-code-foundations/lessons/welcome-to-codecademy/exercises/change-physics
Can anyone direct me how to finch this first lesson?
Thank you