Accept what you can't control.
Control what is in your control, and accept what is not.
The tricky side of this is; accepting what you can't control.
To put it trivially, if you can't control it, no amount if time, effort, or energy will change it. Which is what makes it "out of your control".
For example, to be current, your holiday being cancelled due to new restrictions.
Another example is the past. You, right here in this very moment, cannot control what has already happened.
Sometimes when you recognise that something is out of your control, it takes a level head and a deep breath to remind yourself that there is nothing that you can do.
What you can do is control the way that you react to what's out of your control.
The quote I had above my schedule during isolation; "Things turn out best for people who make the best of the way things turn out.".
Keep a level head, play the cards that you are dealt, and control what is in your control.