Can be replaced. I know there's a company in The Netherlands that replaces them. (results in a slightly heavier fork as they cut away the broken part, put a smaller tube in what's left of the original and than slide a new one over this smaller one).
It's more a hairline crack and it has not gone through to the steerer, mayb a resin can fix it?
Probably one of the london carbon repair shops can repair it locally than sending it all the way to Europe, especially with the postal service happening atm.
Anyone has experience fixing a cracked carbon steerer?