The parking brake is just a catch that holds the foot brake/ clutch in the on position.There is a little spring which may have broken or fallen off.
As you have the model number go to the Husqvarna web page & download your parts book.
You can not reach under cause the catch is on the top.
You will need to take the battery out to see how it works, very simple.
And of course you will need to be bitten by a vampire so you can hang from the rafters to hook it back together cause that is about the only way to get in there.