First, your broadcast name and password may be on a label on the base or side of the router. It may also be in some documentation that came with the router (this assumes you have not changed it).
Or you can "logon" to your routers admin pages and reset the password there. The documentation should be tell you how to logon to the admin pages and the userid and password.
But dont get confused.
Your router has a broadcast name and password, and also an ADMIN userid and password.
The broadcast name and password is used to connect devices, like your tablet or smartphone, to the router.
The ADMIN userid and password is used to logon to the admin pages and reset settings such as your broadcast password. You normally do this via your browser (you use your browser to look at your router admin pages).
Once you change your broadcast password you will need to use it all on devices (if you have used a smartphone to already connect to your router for example).
It is a good idea to ALWAYS write down important userids and passwords for ALL devices. If you don't have to enter them regularly it can be easy to forget them. I have all my important userids and passwords written down and hidden away.