I wasn't able to find earnings by major. Do those data exist in the database? If not, have you considered collecting them?
Scorecard does not provide earnings by major/program of study. Earnings data are collected by matching student grant and loan data to tax records and past student grant/loan records do not have this level of detail. However, recent changes in student grant/loan reporting might allow this in the future.
The site has a data dictionary here that you can search for what you want. It does not contain major in this version. It does contain some degree fields. Good luck.