First and foremost, you must prove that your illness arose out of the course and scope of your employment; it is not enough for you to think it did. Insurance companies typically deny Covid-19 cases under the guise that Covid-19 is a sickness that the general public is exposed to outside of work. You must show that there is a link between Covid-19 and your employment with hard evidence, with expert medical evidence supporting the link. The law presumes that firefighters, peace officers, and emergency medical technicians may be exposed to Covid-19 while on the job.
If applicable, it's crucial to establish how other employees in your department have tested positive for Covid.
You'll also need to show that you were exposed to Covid-19 at work and that you contracted Covid-19 as a result of that exposure, as well as how this differs from any exposure you may have had in the general public.
Unfortunately, exposure to Covid-19 while at work is not enough, other considerations include; if someone in your household had Covid-19, whether you attended places where you were exposed to Covid-19, and how your employment exposure compared to that of the general public.