If you want to move the forum to another directory/domain, then it is necessary that you adjust the directory/domain under System -> Packages -> Manage Applications.
It is important that you proceed in the correct sequence, otherwise you will throw yourself from the ACP. First, change the path of all installed applications (except the primary) and then the WoltLab Community Framework. Only at the end edit the primary application.
Note: If you change the full domain, then the cookie domain must be changed to the new domain also. The entry is identical to the domain under domain settings.
Thrown from the ACP
If you have taken the wrong order and have been thrown of the ACP, then you can change the paths with phpMyAdmin directly in the database in the table wcf1_application. In order for the change to take effect, you must also empty via FTP the directory /wcf/cache/.
Directory/Domain already changed
If you have already changed the directory/domain and now the old directory/domain are passed when calling the forum, then call the ACP via direct link. To do this, add to the usual forums address the path /acp/ (e.g. example.com/forum/acp/).
Then proceed in reverse order to the instructions above. So you have to start with changing the primary application.