Why kinetic energy is considered constant in definition of electric potential | Physics

In this video, I have tried to explained the text-book definition of electric potential, which says that electric potential is amount of work done by an external force to bring a unit positive charge from a reference point to a point in the electric field.

Watch this video as a prerequisite:
Work and Energy:

Potential energy,electrostatics,conservation of energy,work and energy,kinetic energy,coulomb's force,electric field,physics,iit,