rpi and other sbc are not that reliable in the long term. short term is great but they tend to fail in the end... the local balance refers to the liquidity beeing on your side of the channel if you close them you get them back on chain in your wallet associated with the LN client
I am moving away from RPI asap onto better HW, but to bootstrap and learn its good I think. In thunderhub (my personal interface choice), go to channels and click the "x" on the channel you want to close. I would advise against doing a force close if at all possible.
im running umbrel on a rpi currently. I have also used raspiblitz and enjoy interfacing with the terminal, but I am currently attempting to make a decent node and figured ill use the gui tools that have been created