In this article you will find a lot of useful information. We like the APPLE technique:
Acknowledge. Notice and acknowledge the uncertainty and anxiety as it arises in your mind.
Pause! Don’t react as you normally do. Don’t react at all. Pause and breathe.
Pull back. Tell yourself: “This is just the worry talking, and this need for certainty is not helpful and not necessary. It is only a thought or feeling. Don’t believe everything your mind tells you. Thoughts are not statements of facts. They are just thoughts.”
Let go of the thought or feeling. It will pass. You don’t have to respond to them. You might imagine them floating away in a bubble or cloud.
Explore the present moment, because right now, at this moment, all is well. Notice your breathing and the movement of the breath entering and leaving your body. Notice the ground beneath you, and gently push your toes into the ground. Look around you and name 5 things you can see, 4 things you can hear, 3 things you can touch, 2 things you can smell. Right now.
Then shift your focus of attention to something else—on what you need to do, on what you were doing before you noticed the worry, or do something else—mindfully with your full attention.