If you hold down your finger on the HomePod that you want to make the main HP, and initiate Siri(be sure to ask a question and let her finish the answer - ask the current temperature or something), then that HP will become the one that will answer "Hey, Siri" requests, which then is the main one.
I know for a fact that will switch which HomePod becomes the main one, however, if for some reason that arrangement does not work out for you, you could always just unplug and move the one by the entrance to your living room to where the other one is, and vice versa. That should also work, but this option would be your last resort option as I know what I explained up above will change which HomePod will be the main one.
Let me know how it goes and if there is a problem, just let me know and I will try my best to help you figure this out!
Edit: What is odd is that my iPhone 12 Pro Max will let me transfer to both HomePod Mini's. I know in my earlier post I said it wasn't letting me do it then, but there is definitely some bugs in the software so sometimes I go into settings and hit restart, which will restart both and that seems to fix issues like that, and obviously in this case did fix it because I just did Handoff to first my main HomePod Mini, then transferred back to my iPhone, and then did Handoff to my non-main HomePod Mini, so that even kind of flustered me a bit, why last night it would not let me do it, but now it is allowing it...had to be the restart.
Also, what type of HomePods do you have? The original HomePod(s), or the HomePod Mini(s)? End Edit.