Testing. There is testing for each which revels which it is. We shouldn't guess at it. :>)
Of all the symptoms they list for Covid-19 (not just the main ones like shortness of breath, inability to smell or taste things, and coughing), surprisingly sneezing and runny nose are not on the lists very often. I think at this time of year sneezing and runny nose alone are more likely to be allergies.
Most people I know go get tested in that situation. In my case I would get tested if I knew I had been in a high risk situation. Otherwise I would lay low until specific symptoms develop such as fever, weakness, cough and loss of smell and taste.