I am getting confused by this thread now. I read the email and the parts on the website as stating the 'free' extension part starting at the point of your next tier point collection date e.g. November 2020. That means you keep what ever level you are on now until that date and then they will extend it to November 2021.
At your next tier collection date, you will then start on your renewal for the following year as if it was normal to build up your tier points for it, except they are giving 25% reduction at that point. So in the November example, the period of 9th November 2020 to 8th November 2021 you just have to meet the respective levels to get it renewed to November 2022.
So again using the example above, you do not need to do anything until November 2020 and just start work on it from there. This makes the most sense from what they stated anyway...