Question

what effect do two parallel wires carrying currents in the opposite directions have on each other?and How?​

Answer 1

The magnetic field of the left-hand current causes a force on the right-hand current that is a repulsion so we know -- from Newton's Third Law -- that the two currents repel each other.

Answer 2

it will change their respective magnetic fields, which will also change the direction of current and the direction of force