Hello I will help you with your question,
To remove the Valve,
Remove the bolts from the base
Use carb cleaner to remove the carbon in the base of the valve and the passages in the mounting surface. You will have to remove the plastic engine cover to reach the valve.
You will have to judge the condition of the gasket once you see it. You may be able to reuse it or if it is torn or burnt you will have replace it. It is possible to install the valve backwards so note the position in the picture for proper orientation.
Let me know if you have questions