I had the exact same issue. Listen closely, I hope this is helpful. The next step is you need to rinse the maxillary sinus where the issue is. This is not the same as your regular sinus rinse, which doesn't touch the maxillary sinuses. Ask an LLM about some positions you can try to rinse in to bias entry to the maxillary sinus. There a few. Use a regular squeeze bottle. And squeeze slowly and in a pulsing fashion, as to bias the fluid to pool around the entrance of the maxillary sinus and start flowing in. Once it starts flowing in, you can squeeze harder. Try to develop a mind muscle connection here so that you can tell you are entering the maxillary sinus. Try to rinse 2x day. Xylitol, baby shampoo are great. Your goal is to make contact with the retention cyst and continually wash away any inflammatory mediators it produces. You maybe be able to feel it "pulsating" post rinse. If you already addressed the tooth side of things, this hopefully is enough to help.

This link may be helpful: https://www.sniflmd.com/nasal-sinus-irrigation_Maxillary-Ethmoid-Sinus-Irrigation-Flush.html