Discuss with your manager and find out why. Ask them to be honest with you. Ask if it is something you can change. Maybe they just negotiated a better salary

Discuss with your manager and find out why. Ask them to be honest with you. Ask if it is something you can change. Maybe they just negotiated a better salary than you did. Maybe they have experience that you do not. If you do not agree, you could skip-level to their manager if your company supports that. Beyond that, if you are not satisfied with the answer, consider looking to other opportunities without hinting this to your current employer.