Question

How internal forces can create a torque ,angular acceleration and rotate a body?

Answer 1

If the object is rigid, then internal forces can't change the momentum or the speed of the object (either linear or angular).

While you can model the object as having certain internal forces, and you can see that those forces might create a torque, there will always be additional forces in the other direction that create an opposite torque. Altogether, the sum of torques about the center of mass from internal forces will be zero. Therefore, we usually ignore such forces.