The default is "sololink", but if you changed it and then forgot it, you'll have to perform a factory reset. As the Solo User Manual (rev 9) says in section 2.7.4, "If you forget your SoloLink password, perform the factory reset procedure described in Section 10.7 to reset the password to the temporary password (sololink)." If you need to perform a factory reset, and also lost your copy of the User Manual, it's available HERE.