Think of yourself as dead. You have lived your life. Now take what's left and live it properly.
Life likely hasn't been perfect for almost anyone, but would you rather die right now (with likely unfinished desires, wishes and more regrets) or would you try to make the best use of what you have?
(It may be a bit difficult to fully live as per the quote even if you're already familiar with stoicism - it's quite hard for me too - but something that sometimes helps me is to literally visualize yourself dead as of now.
Maybe a stroke.
Would you be happy?
If not, you should do something about it.)