Most blocks are set by the admins of one community, and only stop you from editing or chatting on that one wiki. The name of the blocking admin should be on the block notice you see when you try to edit there.
You may be able to contact the blocking admin by leaving a message on your message wall. This is usually still open to blocked users and changes will usually be seen by others in the community. Your message wall can be found under the profile menu at the top right of any page. You can also contact the admin on their wall on Community Central.
However, if these options are not possible in your situation, then the best advice we can give you is to wait for the block to expire or join one of the hundreds of thousands other Fandom communities available.
If your block is global, please contact us.
Note: in order to look into your global block, we'll need some additional info. You can find this info when you try to edit a page or leave a comment - you will see a message titled "Your username or IP address has been blocked", like this:
Please copy and paste the content of that box, or send us a screenshot. At minimum, we need to know the block number, which will be labeled "Block ID" in that box (you may need to expand the box or scroll down). Just let us know that information and we will look into why you are blocked.