Imam Assim al-Hakeem dispels misconceptions about proper index finger movement during prayer.
Some say the finger should be moved upwards and some said you should do that without moving your finger. Some of them said that we should only raise it (finger). And some said it should be moved upwards. And some said you should move it whenever you supplicate.
It’s simply states that he (Prophet Mohammad) used to point his finger from the beginning of the sitting position till the end. Moving it not up and down rather moving it moving it in its place as if it’s shivering or shaking. And you do this throughout the prayer.
At the end of the day even if you don’t raise your finger at all from the beginning till the end the prayer is valid because this is a Sunnah.