To update the ECDSA host key, you can remove the cached key for the IP address of the server on your local machine using the following command:
ssh-keygen -R <IP address>
This will remove the old key from your known_hosts file.
Alternatively, you can update the key instead of removing it by using
ssh-keyscan -t ecdsa <server domain or IP address> >> ~/.ssh/known_hosts
This will add the new key to your known_hosts file and hash the hostname/address.