I tried to change it in the settings and it matches what i have written down. I tried 2 different browsers, chrome and firefox. Tried clearing my cache and history. I do not know what else to do?
I think you just forgot it. Email plex them self. They should be able to just replace your pin. The one you lost.
Thank you. What is the email address?
Alright go to this link https://support.plex.tv/hc/en-us?mobile_site=true. Then pick your issue and summit it. They’ll ask for your email give your plex pass email. After which they will get back to you soon as they can. 
It’s not hard. I have done it myself. 
You can edit your Plex account PIN here: https://plex.tv/users/edit
If you are the only user on your server and you are not planning on inviting other users into your Plex Home, you can erase your PIN. It is not necessary then.
If you however are talking about the 4-character code which is used to ‘link’ Plex clients to your account, these are to be input here: https://www.plex.tv/link/
(you have to be fast - after you are shown this code, it is only valid for a very few minutes)
