there seem to be a couple ways (i found java examples, but b4a should be similar):
intent = new Intent(android.provider.Settings.ACTION_SECURITY_SETTINGS)
startActivity(intent)
startActivityForResult(new Intent(android.provider.Settings.ACTION_SETTINGS), 0)
but if user has already said she doesn't want to grant permission, why would you send her to the settings? you might want to explain what's going on and then offer the chance to reconsider (and if she says OK, then run the intent). i usually tell people (who have not granted a permission) that certain features will not function unless they grant permission, which they can do at any time by going to system settings, etc. by automatically sending her to the settings, she just ends up going back to your app even if she still hasn't granted permission...