Take the passage away from the piece and practise it alone.
Try doing the pattern up and down on the scale of C.
1,2,1,2,1 on C
1,2,1,2,1 on D etc
Try slow, fast, staccato, with a different rhythm, with a metronome, without a metronome, standing on your head
Keep your hands and wrist flexible and try not to stiffen up.
Also, you could do it on your lap or table when you are away from the piano.
Be patient with yourself. It'll come