How do I go about suing Uber if this is the second time a driver has stolen from me?

File a criminal complaint with the police.

If the driver actually stole from you (such as taking items out of your pocket or purse) you probably can sue Uber. If you left items in the car, it is reasonable for the driver to insist that you come and get the items, or pay for the driver to come to you. You cannot leave items behind, and then shift to the driver the cost of the ride to bring things to you. The cost of suing would be far more than the cost of paying the driver to ride to your location, and filing a lawsuit is not a guarantee of victory.