i recently got my flute back after about 5 years and i`m excited to start playing again.
however, i`ve forgotten a lot of the warm up exercises.
i remember one where you`d play the same note, different octave, but that`s about all i can remember.
can anyone help??

you may play some simple short pieces of music to warm up . I suggest you should also practice at least 30- 60 minutes a day, 5 days a week, in order to take up the flute again.
Playing the "silent night " is a good idea as X`mas is coming !

Good Luck.

Try playing scales up and down, arpeggios, long tones, select one note go down from tone to tone returning to that one note. There are many different methods.

I mainly play the Bb and Eb Major Scale with arpeggios and thirds and play and hold high notes.