i have forgotten my activation 4 number code when my macbook air was missing now that i found it how will i unlock it?

I don't know if that works for what the OP needs. I think he is saying that he set a 4-digit passcode lock on the Mac just as one can set on an iPhone. The link you posted is OK for a normal Admin password, but may not work for the passcode. I've never tried it. Have you given it a try?

There is no iPhone. I never said there was. I said, he set a 4-digit passcode lock on the Mac just as one can set on an iPhone. "Just as" means "like." It is possible to create a login shortcut code so you need not enter a long password. At least I think so because I remember doing it once.

Try Bypass and reset the password on any Mac in no time - CNET

Where in the original post is there any mention of an iPhone?