Okay, instead of going through all the folders just search for the file because there's two files of the same name and one of them would/should contain your restrictions passcode.
To browse your backup you simply just click on the left hand side where it says where your device backup is (Folders)
Your passcode should be close to the 'SBParentalControlsPin' line
I used this on my IOS 7 device idk if it's the same for iOS 10
There's also a case where there is no 'SBParentalControlsPin'
In this case you'd need to put a line of code for it
I forgot how it goes
Probably something like
<key>SBParentalControlsPIN</key>
<string>xxxx</string>
Change xxxx into the pin you want
Put it under the line
<key>SBParentalControlsFailedAttempts</key>
<string>X</string>
Once you've edited the file in the directory just restore it on your phone then reboot (pretty sure it re springs the device for you)