How to close airports

Hello everyone: I have 3 offensive airports I want to close but I dont know how. One in a slave and two in a C3. What should I do to close them?

If they are offensive airports then go to offensive weapon forces page and click destroy weapons and bases and you should just be able to destroy them to 1 base

If they are offensive airports then go to offensive weapon forces page and click destroy weapons and bases and you should just be able to destroy them to 1 base

Thank you very much, Sheepman!