Need some query help.....

I'm very new to Access. I was wondering how I could display a field in a
query that is conditional. I will do my best to explain...

I want to add a field to my query that grabs the info from Project.Badge or
Project.BadgeET depending on if the field TestType is displaying "Eng" or
"Pkg"

so it would be something like this

If TestType = "Eng" then
Display Project.BadgeET
ElseIf TestType = "Pkg" then
Display Project.Badge
End if

im assuming I would type some formula in the Criteria section?? but under
field, i can only select Project.Badge OR Project.BadgeET, not both.

Thanks in advance for the help.