what to Do when you found a kufir doing tabligh with to a muslim?

One should intervene, and explain to the Muslim the harms and receptions of
the Kuffaar. It is the duty of the Islamic government to expel such
missionaries.

Insha Allah, when the Taliban return they will revive the forgotten duty.

and Allah Ta'ala Knows Best

Moulana Imraan Vawda
FATWA DEPT.

CHECKED AND APPROVED CORRECT: Mufti Ebrahim Desai