Not as simple as that, you may be lucky and get a gas burner to fit, but you cannot adapt one to fit if it is against manufacturers instructions.
- chimney MUST be swept, when changing from solid fuel to gas.
- flue liner may need installing, depending on the condition of the flue brickwork and the manufacturers instructions for the gas burner you purchase,
- Terminal ? again manufacturers instructions will tell you whether you need a pot with bird guard, or a cowl.
You will also need a gas fitter with LPG qualifications, not all have them.