What should a person do for a minyan in quarantine? is he allowed to tune into 770live.com and answer Borchu and Kedusha?
Teffilah Betzibur can be done by joining in and Davening at the time the Tzibur are Davening. Preferably at the time you know a specific Minyan is Davening, such as via 770live.
You can answer Amen, Kaddish, and Kedusha on 770live, over the phone (718-682-0770) but not via the website, due to a short delay.