Touch controls from scratch aren’t super easy. I would recommend using the built in joystick interface if you’re new. If you absolutely can’t, then the first thing I would do is learn to use the input touch node.
This generates events when you press/move/release, so you don’t have to use tick. You can then store which finger pressed down and how it moved. Keep in mind that your rotating finger could be finger 1 if you’re not already touching the left stick, or it could be finger 2 if you are already touching the left stick.
As for calculating the rotation itself, you will need to use the “moved” and “pressed” vectors to “Find Look At Rotation”. This will give you a rotator that you can plug into “Set Control Rotation”.