Hello @Ashfaq Naina A 

Regex to use: Host=([^,]+)

Follow these steps:

1) Go to Event Rule → Field Mapping
2) Set: 1) Source Field: additional_info
2) Target Field: node
3) Enable "Use Regex"
4) In Regex:
1)Enter: Host=([^,]+)
2) Set Group = 1

Please click helpful if it helps you 

Regards