According to the World Health Organization:
“The likelihood of an infected person contaminating commercial goods is low and the risk of catching the virus that causes COVID-19 from a package that has been moved, travelled, and exposed to different conditions and temperature is also low.”
You can read the World Health Organization's information on COVID-19 here: https://www.who.int/health-topics/coronavirus
If you'd still like to cancel, you should contact the seller directly via onsite messaging. If the order is unpaid, the seller can cancel the order on their end. If the payment has already cleared, you can simply request a refund with a note to the seller.
More common questions on COVID-19