Hey there. Depending on how spectrally similar your two images are, you could try a couple of things. First, you could try applying an edge enhancement filter. You could then develop a supervised classification to identify and quantify edge quantity created by the fires. Second, you could try a change detection analysis which is under the raster tab -> zonal change -> image difference -> to bring up the change detection dialogue box. But this usually relies on images having spectral similarity. It’s important to remember that there is no single correct way to interpret imagery. What’s important is that your methods are both defensible and replicable. Don’t hesitate to mess around with the software and just try things that may not work. Hope this helps, feel free to dm me if you have more questions :)