First you'll need to install and run a Tor daemon on your device.
Inside the Sparrow terminal, go to to Preferences -> Server -> Edit, and then select whether you are using Bitcoin Core or Private Electrum. Select Continue. On the next screen go down to "Use Proxy?" and select "Yes", in "Proxy URL" put 127.0.0.1 on port 9050. This will route all external Sparrow traffic via Tor.
Excellent set up, by the way. Your own node, own Electrum server, Sparrow, all via Tor, endless free coinjoins. Which Electrum server package are you running on your Raspberry Pi?