You should create file <arbortext_install_dir>\adapters\com.ptc.prowt.arbortext\siteprefs.xml. Best way is to create a copy from file "siteprefs_template.xml" is localted in same dir.
Next you should define Windchill server name. Open siteprefs.xml file, find element <parametername>HostList</parametername> and his child element <parametervalue>.
Define server name in format: Name|Windchill connection URL, like in example below: