What do I do for lump same size in both breasts?

Serious. Depends, on age, family history, physical exam, mammogram, biopsy. There are bilateral benign and/ or malignant lesions. Absolute diagnosis is required. Early diagnosis and treatment are imperative.
Atlhough this may. Be part of underlying structure - it would be prudent to have this checked to insure that you don't have bilateral breast masses. Med eval.