My Honda Civic 1.7 LX has a rough idle and at times it will die down to 500 RPM how do I fix this and what is it caused from

Could be any number of things as your symptoms are quite generic. Dirty injectors or air sensor. Plugs , plug wires. What year? Could have a dirty air filter. Check engine light on? Codes?

Consider cleaning the Idle Air Control Valve (IACV) and increasing the idle speed, by loosening the inside 12mm stop nut and taking up on the outside 12mm adjusting nut on the throttle cable bracket. Without knowing more, this is what I would suggest.