Welcome to ask.fedora, and thank you for starting off with a good question. I don't think that Fedora supplies any Helvetica fonts, probably because of licensing issues. About the closest that you can find in the standard repos is mgopen-moderna-fonts.noarch and installing it will bring in mgopen-moderna-common.noarch as a dependency. This will give you the regular, bold, oblique and bold-oblique forms and most people will never notice the difference.