After you’ve tuned your flute successfully, you’ll need to learn some of the quick options for changing the pitch of a note so you can make tuning adjustments while playing.
One good principle to comprehend is that as you cover more of the tone hole on the flute the pitch goes down and conversely as you uncover the tone hole the pitch rises.
With this is mind while playing a B (middle line of the staff) lower your chin, allowing your bottom lip to come across the tone hole more; you’ll notice the pitch goes down. Lifting you chin and uncovering the tone hole will raise the pitch. Basically you are allowing your bottom lip to cover more or less of the tone hole.
Have some fun on different notes bending the pitch up and down. See how quickly you can do this and how far you can alter the pitch. You’ll notice there is more scope to lower the pitch than raise it using this method so it is better to be tuned a smidge sharp, needing to bring the pitch down, than to be a bit flat and constantly needing to lift the pitch.
It is better to make these adjustments with subtle head movements rather than turning your flute in and out with your hands. Ideally the flute will stay quite still while your head does the adjusting.