In 1875, where did Dayanand Saraswati formally organise the first Arya Samaj unit?

The most characteristic feature of the Arya Samaj is the emphasis it laid upon the work of Suddhi. As a matter of fact, this aspect of the Arya Samaj excited the greatest interest in it among the people outside its own ranks. Suddhi meant the reconversion of those Hindus who had once been converted, willingly or forcibly, into other religions but who were now willing to come back to the fold of Hinduism. The Arya Samaj looked upon Suddhi as a potent instrument for effecting the religious, social and political unity of India.