self-styled or so-called, often used to describe someone who claims a title or status without having the legitimate authority or qualification.

स्वयं-प्रघोषित

English Usage: He is a soi disant expert in the field of quantum physics.

Hindi Usage: वह स्वयं-प्रघोषित क्वांटम भौतिकी का विशेषज्ञ है।