Eat low carb, keep your blood sugar low. Colgate Total mouthwash has the active ingredient shown to kill Covid in vitro, Listerine doesn’t. Zicam nasal swabs works on colds and I used them to great effect when I had the alpha variant.
Killing it in your upper respiratory tract is how you keep it out of your lower respiratory tract.
For Colgate, is the ingredient Cetylpyridinium Chloride? Phillips Sonicare mouthwash has it too, and zinc as well