Question

how did mahatma gandhi converted national movement into mass movement

Answer 1

Mahatma Gandhi took charge of the movement from 1915 and started a Satyagraha movement against the Rowlatt Act in 1919-and the violence following the Jallianwala Bagh massacre, he called of the movement.
Gandhi made the movement truly national by bringing in more Muslims by supporting the Khilafat Movement.
The non-cooperation movement was started with the middle class refusing to buy British cloth and boycotting Government offices, schools and courts.
The peasants in Awadh, tribal also joined in the non-cooperation movement which was called off because of the violence in Chauri Chaura.
In December 1929, under Nehru’s leadership the radicals won over the liberals and the moderates and formalised the demand for Purna Swaraj and not Dominion Status as had been thought of before.  

Answer 2

Mahatma Gandhi took charge of the movement from 1915 and started a Satyagraha movement against the Rowlatt Act in 1919-and the violence following the Jallianwala Bagh massacre, he called of the movement.
Gandhi made the movement truly national by bringing in more Muslims by supporting the Khilafat Movement.
The non-cooperation movement was started with the middle class refusing to buy British cloth and boycotting Government offices, schools and courts.
The peasants in Awadh, tribal also joined in the non-cooperation movement which was called off because of the violence in Chauri Chaura.
In December 1929, under Nehru’s leadership the radicals won over the liberals and the moderates and formalised the demand for Purna Swaraj and not Dominion Status as had been thought of before.