Saying “I don’t know, let me find out” at work beats guessing wrong with confidence.

Confident guessing is the expensive kind of wrong. Say you are not sure and the cost is a few seconds of looking less polished. Guess and sound certain and someone acts on it, and then the error has travelled before anyone catches it. The people around you are not grading your confidence, they are relying on your accuracy.

Practise the actual sentence until it comes out easily, including the second half, which is the part that matters: you will find out and come back. Then come back, even when nobody chased you. Two or three rounds of that and people start trusting what you do say.