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From the support documents:
Reset your Slimline remote 2
You can return all advanced functions back to their original factory settings by resetting the remote.
Press options button for a minimum of 3 seconds; the green LED next to the Optik power button on the remote control will flash twice.
Enter code 9999 ; the green LED next to the Optik power button on the remote control will flash twice, indicating that the remote has been reset to the original factory settings.
I am not aware of any means to adjust the PVR volume with the newer Slimline 2 remote. I seem to recall you could with the older Slimline one.