Groovy expression to categories based on the email subject and email body

Summary:

Hi Team,

We have requirement to categories the SR request based on the email subject and email body,I am creating the logic under triggers with the triggering event as Before Insert.

I ran the below code but it was throwing validation error as email subject and email body is not part of the fields under HR helpdesk request -->fields --> custom and standard. Could you please let me know a solution on this asap.

if (EmailSubject?.contains("Hello World") &&
EmailBody?.contains("abc@yopmail.com")) {

Category2_c = "Medicals"

Category3_c = "HR"

}

Could you please provide me a solution on this ?