I forgot my MacBook Air password

I have a MacBook Air and I have not turned it on since I change internet provider and I forgot my computer password. I purchased a ethernet adapter but when I connect it, it shows that there is not internet connection. I am guessing it does not recognize the new internet service. What are my resolution. I tried to make an appointment via online with the Genius Bar but I cannot see where they are allowing you to do so. I guess I will walk in. I tried doing a telephone call but she had the same issue as I discussed above.

[Re-Titled by Moderator]