It adjusts the toe of front wheels and it's called DAS (Dual Axis Steering). This is only currently being used by Mercedes in F1. In simplest of terms and from what I have understood, it can reduce friction and tyre wear on long stretches by having 0 toe (parallel front wheels). And achieve better grip on corners by moving the front wheel outwards.

This is a nice video explaining all this: https://youtu.be/TxKhi6Qsrog?t=67