Here is a guru whose name I don't know who attracted crowds during the Kumbh Mela, thanks to his wisdom or his small size.
There is no authority empowered to grant this title; Hinduism - without an ordered centralizing authority - has no Church, no clergy, no training school for future gurus. It would be inconceivable for someone to proclaim himself guru, because it is the public recognition of the level of inner achievement that suggests that this or that has the stature of a master. The recognition of the status of guru is only obtained by the guru registered in a long line of transmission and who will be considered able to recognize the ability of the disciple to teach in turn.
There are cases of guru who have not received the title of another guru. In this case, the public rumour plays its part: we come to listen to it and if a few people say they are disciples, and it's OK for everyone. "