Factory Password
D-LINK DSL-5300 factory password can be found on the sticker at the router bottom
Check also D-LINK DSL-5300 default ip.
Check also D-LINK DSL-5300 factory login.
If you want to reset your router password to the factory, check how to Master Reset D-LINK DSL-5300, but be careful because this also reset all your router settings!

https://www.hardreset.info