At this point you have a few options:
- attempt to activate Fireworks via the methods mentioned in other related threads in this FW community forum. You are on your own: various possible solutions that do not seem to work for everyone and for every case or context.
- install a trial version that works for 30 days and convert your files
- open your FW files in Photopea, and save as a Photoshop PSD file, and switch to other software. Photopea is a free online Photoshop clone.
To be honest, I use a cracked portable version of Fireworks to open legacy files. I purchased Fireworks CS6 legally years and years ago, and it stopped working. None of the various methods (described here in various threads) to activate FW worked for me, and since I have the license to install it, I have no qualms over using a cracked version.
That said, I only use that verson to convert old files once in a while. Fireworks is defunct and it's been abandoned and discontinued by Adobe over a decade ago. It is time to move on. It doesn't work on Macs anymore, and I wouldn't be surprised when it stops working sooner than later on Windows next.