What do quantum eraser actually do? From what I know it basically erases which path information so even though the detectors still interact with the photon, but not able to tell which path the photon takes the result is a interference pattern. So what actually did the eraser do to the photon, does it revert the localised wave back to superposition state? Also this which path information, how is it stored in a photon?
 A: *

*It is called spontaneous parametric down conversion, creating entangled photon pairs.

*One of the entangled photons goes directly to the detector, the other goes through a double slit mask. Both detectors are connected to the coincidence counter, making sure only entangled photon pairs are counted.

*A circular polarizer is placed in front of each slit, one creates clockwise, the other creates counterclockwise polarization for the photon passing through the slit, thus marking the photon, destroying the interference pattern. This is how the which path information is stored in this photon.

*A linear polarizer creates the other photon (that does not go through the slits) diagonal polarization.

Entanglement ensures a complementary diagonal polarization in its partner, which passes through the double-slit mask. This alters the effect of the circular polarizers: each will produce a mix of clockwise and counter-clockwise polarized light. Thus the second detector can no longer determine which path was taken, and the interference fringes are restored.

https://en.wikipedia.org/wiki/Quantum_eraser_experiment
So you are correct. You say it reverts the localized wave back to superposition state. What is correct to say, is that the diagonal polarizer erases (alters) the effect of the circular polarizer, thus restoring the interference pattern.
