Confused how to derive output voltage from Op Amp and RC circuit
There are hidden power supplies connecting from the ground node to the positive and negative supply pins of the op-amp. Current to the output pin of the op-amp flows from these supplies.

I'll redraw the circuit including these supplies:







simulate this circuit &ndash; Schematic created using CircuitLab

Now can you see how current from the op-amp output can flow back to the op-amp's positive supply pin?