Hello; I do get that the information around keeping a tank is overwhelming at first. Let me say this; the thread has the basics laid out within the overall content. A few members have summed things up in a fairly short form. I and I think others have posted links on the relevant topics. If you have not taken a look then perhaps such will help.
You have made a decision a while back in a post. That being the choice to try to save the current fish if such is possible. Once that decision was posted I changed my posts a bit from how to cycle a tank over to how to reduce the damage to the fish from ammonia exposure. Such is why i suggest WC of around 50% every two days along with the use of PRIME or SAFE. This may help the fish immediately because of the fresh water and that the PRIME locks up the ammonia. This very likely will slow down or perhaps even stop the growth of the BB. This is one path. There are others.
A different path is to do fewer WC and use less PRIME and allow the ammonia to build up in the tank. This will promote the growth of the BB colonies and get you to a cycled tank sooner. Will be harmful to the current fish of course.
Another path is to tear down the tank and sanitize it and the equipment. Then start over with a fishless cycle. This path may become a choice if there is a pathogen in the tank.
Do a search online about cycling a tank. Do a search on this site about cycling as there are multitudes of threads on the subject.
But doing something different is an option.
Good luck
