Go to
http://laanx.fragnetics.com/register/ and click "Forgot my password".
You can also save the file
planeshift.cfg before uninstalling Planeshift. Password is stored there in encrypted form (on the condition you checked option "remember password" on login screen), so after reinstallation you must only restore lines starting with:
Planeshift.Connection.User
Planeshift.Connection.Password
Or just put your saved planeshift.cfg in new PS directory if You are lazy
