Hi,
Can you try the following step?
strBody ="Hi,
Please find the attached file.
Regards
{0}"
Then
string.Format(strBody,varBotMAchineName)
This will replace {0} with content of varBotMAchineName.
OR Create HTML Content activity might help you.
https://docs.uipath.com/activities/docs/create-html-content
Regards,