Try this if not take in to Apple.I am getting the blinking +/- since 3 days now. I cannot reset (either manually turning off and on again waiting for the red dot and three beeps or using the Home App). Nothing works. Is there any possible fix? I can only assume that this has happened due to one of the recent software updates. Which if true means I have a very expensive brick thanks to Apple. That is pathetic. I fear the only way to try and resolve this is having to waste half a day going to the nearest Apple Shop and arguing with them that my homepod did not jump off the shelf in the middle of the night and self-destruct.
Reset HomePod or HomePod mini – Apple Support (UK)
Find out how to reset your HomePod or HomePod mini to its factory settings before sending it in for service, selling it or giving it away.