First: A lot of streaming services, such as Twitch, have delay auto added due to how they choose to encode videos. In most cases, Restream will only add about 2 seconds of delay to your cast. To see if Restream is causing this delay, attempt streaming directly to the delayed service to see if the delay is the same.
Second: Change to a different Restream Server, you can do this by selecting a new RTMP URL on the dashboard or within broadcast software that supports Restream.
Third: Contact the Live Support team on your Restream Dashboard.