yeah start medicating if it's not showing improvement.
just to clarify though, i have experience using parasite clear to clear parasites, not for what's happening to your bichir. the antibacterial property in paraguard may be helpful since we don't know what's causing it. as long as it's not getting worse and your bichir's not negatively affected by it, you have time to try different things, so if you have parasite clear, by all means.
you sure there's no signs of tiny flukes on the belly?
if you're so incline, another thing you could try in combination with either parasite clear or paraguard is to take the fish out and put some neosporin on the red area as an antiseptic. apply liberally. i'm not sure how big the bichir is so it may be easier said than done haha