The second mind changing has two parts: one is as you already heard, a contemplation on impermanence, and the other is to reflect on our own death. Since everyone who is born will die and the exact time is unknown, this reflection can help us live today as if we did not have long to live. If we can really take this to heart, each new day becomes a gift and the extraneous distractions can more easily fall away. I would like to take my last few breaths in this life knowing I had fully jumped in while here. In order to die well, we will need to learn how to live well.
At the time of death, our only support will be our state of mind and what we have consciously cultivated. To contemplate the uncertainty of when we will die is meant to undermine any complacency or tendency to take this life for granted, and propel us to develop awareness without delay.
Reflect on someone you know who has died and recall if it seemed unexpected, like they would always be around, even if they died slowly. Just as this person was here one breath, and then suddenly gone, see how you feel about recognizing that will be your future as well. Does it help you lean into the reality of this precious impermanent life? Does it fuel your desire to live as awake as you can today? Spend five minutes in a yin pose while pausing every few breaths to ask yourself, how am I meeting this fleeting moment? End with the intention, may I have a lucidly awake day, as my simple and complex life is preciously ephemeral.