Since you mentioned you are new to the hobby, I wanted to add a bit of context for what
@AilyNC mentioned about rehoming fish: many large chain pet stores or stores with a pet section unfortunately do not count as "Local Fish Shop"s. Yes they sell fish but to get called an LFS, there is generally an expected standard that you at least try to do what is best for the fish involved and not just derive profit from them. Then again, there are plenty of LFS's that don't follow that ideal, sooo.... But in general, a LFS is a store that specializes mostly or only in fish.
I bring this up because what I have learned is that when large chain pet stores take fish back, they often all go into one holding tank where the individual fish's parameters or needs are not met, and furthermore due to how these holding tanks are set up, the fish are rarely sold and ultimately end up dying
I am certain that you will be able to find a fish store near you that will be able to accommodate the bichir if you do choose to re-home it. An alternate approach is to try listing it for sale on a classifieds page, but it's difficult to know whether the buyer will be knowledgeable either.
I would also second the recommendation on aquarium salt, but would double check that the bichir will tolerate it. I m not familiar with that fish at all, but looking them up just now it seems to me that the reason it is showing aggression is that it is probably feeling crowded in too small of a tank.
Keep us updated on how things progress!
