The plastic is held in on the bottom by the surrounding metal on the seat. You must first come from the inside under the seat cover and foam and squeeze the plastic tongs together and lift the plastic posts out that way. It usually helps to use a socket a little larger than the post to squeeze the post tongs equally. Hope that makes sense. I don't have one out to show you what they look like but once you see one, you get how to remove them right away.

Don't know about honda in particular but I prefer to remove the post, if I can't then I have fitted the cover found the post,cut a small hole and feed around the post although those do look a bit big for that.

I have done those same seats. I ended up prying up gently on the posts and got 3 out of 4 off with no trouble. The 4 one broke around the wide part I pried from. I ended up gluing it and the customer said they would leave the headrest down anyway so it worked out. Not the best or most professional but he said it wasn’t worth spending a bunch of money replacing it.

Actually I think the one with the button has a screw under it now that I think of it. Gently remove the button you push to remove the headrest and the little spring and there is a screw under it. I found out after I broke it lol.

I’ve done quite a variety of seats, and unless those things absolutely need to come out, id advise leaving them, fitting your cover, and then cutting them out last. You got the cover off without removing them, and working around it is always better than breaking them.

Thanks everyone!
I ended up fitting the cover, cutting a small hole, and stretching over.
Next time when I have more time, I'll mess around with removing post.