Hi Jignesh,
You can use a Magma flow that Reads the ‘Position’ channel, then uses two ToScalar nodes to get the X and Y elements (1 and 2 respectively), and finally use a ToVector, passing in the scalar x component, the scalar y component and a Input Value node with a float of 0. That should set the position to [X,Y,0], assuming the particle’s original position is [X,Y,Z].