A 32-year-old multiparous woman at term is in the second stage of labour. After 45 minutes of pushing, the fetal head is at +1 station, in the right occiput transverse (ROT) position. Cardiotocography shows variable decelerations with good baseline variability. The obstetrician attempts vacuum extraction but fails to achieve delivery after 3 contractions with no descent. What is the most appropriate next step?