It isn't clear if "Computername" is part of the field you are trying to extract from or the name of the field. If it is part of the field (assuming _raw)
| rex "Computername - \w+\.(?<Corp>[^\.]+)\.Com"
If it is the field name
| rex field=Computername "^\w+\.(?<Corp>[^\.]+)\.Com"
This assume <host> is at the beginning of Computername. If not, just remove the ^ from the beginning
Both of these assume that there are only two dots in the computername
Thanks for your reply
Computername is from raw dat
But actual field is 'Hostdomain' under which I want to display 'corp' from computername
Computername format - -
<HOST>. Corp. <domain>. com