Stop the service and reset the data
sudo systemctl stop celestia-appd.service
cp $HOME/.celestia-app/data/priv_validator_state.json $HOME/.celestia-app/priv_validator_state.json.backup
rm -rf $HOME/.celestia-app/data
curl -L https://testnet-files.suntzu.dev/download/testnet/celestia/celestia-snapshot.tar.lz4 | tar -Ilz4 -xf - -C $HOME/.celestia-app
mv $HOME/.celestia-app/priv_validator_state.json.backup $HOME/.celestia-app/data/priv_validator_state.json
Restart the service and check the log
sudo systemctl start celestia-appd.service && sudo journalctl -u celestia-appd.service -f --no-hostname -o cat