How do I dispute my guardian claiming me as a dependent?

Sorry if this is a silly or amateur question, this is my first year trying file as an independent. In the 2020 tax year, I lived with my guardian for the first two months before moving out. Fast forward to today, my return was rejected because my guardian claimed me as a dependent for 2020. Is there a way to dispute this claim, and if so, is it possible to extend the tax deadline?