@bowesmana @gcusello @ITWhisperer Thanks for your Ideas for helping me. finally, I did it with the below addition, it worked what i desired results.
| rename host as Server, Name as Message
| eval Severity=case(
EventID="1068", "Warning",
EventID="1", "Information",
EventID="1021", "Warning",
EventID="7011", "Warning",
EventID="6006", "Warning",
EventID="4227", "Warning",
EventID="4231", "Warning",
EventID="1069", "Critical",
EventID="1205", "Critical",
EventID="1254", "Critical",
EventID="1282", "Critical")
| fields Server, EventID, Message, Severity
| search Severity="*$search$*" OR EventID="*$search$*" OR Server="*$search$*" OR Message="*$search$*"
| table _time, Server, EventID, Message, Severity
... View more