For the default H2 DB:
1). Stop H2 DB and Web Console.
2). Backup and remove hawk.h2.db file from <USER_HOME>.
3). Restart the H2 DB and Web Console.
For external DB:
Access to the DB with the proper credentials from DB client, delete the offline agent from table "AGENT"
For Non Persistent Mode:
Remove the corresponding entries in <HAWK_HOME>/webconsole/tomcat/AppData/hawk_agents.xml
---updated-on-May-29-2020---
Webconsole has been deprecated since v6.1. In v6.1 and above, we recommend HawkConsole instead of webconsole. This article is not applicable to HawkConsole.