Hey @Sid – building upon what @JohnRob said, I have some questions too as I think some of the vernacular is being intertwined.
Dumb Switch = Existing Switch ($2 switch you can buy at Home Depot / Lowe’s)
Aux Switch = Special Add-On switch made by GE/Jasco or HomeSeer
In Photo 1 (top photo), it looks like you have a dumb/existing switch (not an aux switch), however in Photo 2 (bottom photo), it looks like there could be an aux switch by GE (hard to tell, but it looks like one).
Also, based on the picture above, I don’t think that is your line as there’s typically two Romex wires that come into the gang-box as the switch needs to switch the line/load on/off.
Can you please take a picture of the other box you have so we can confirm you have a neutral or not?
If you do have a neutral, here is the proper wiring diagram: