Looking for information specific to Coronavirus (Covid-19) - See here
First of all, sorry to hear that!
The organiser individually specifies how and when refunds are to be processed, and in most cases refunds will already be on their way back to you. Refunds may take up to 21 working days but usually take within 5 to appear in your account.
To receive a refund for the booking fee and online card transaction fee, you will need to get in contact with the event organiser (unless otherwise specified).
If the event organiser has explained that the event will take place at another place/time, then it is down to you to ensure that you purchase a new ticket before the event is sold out.