Cast a single person into the platform
There is one role. The photo replaces that person and no one else. Face, hair, build, and clothing should all be visible enough to carry through a moving shot. You do not need to photograph anyone running, and you do not need to copy a pose from the platform.
Two friends in one frame do not become two roles. If you are deciding between people, make two separate results with one portrait each. Permission is required for the person you upload. A picture you do not have rights to use does not become usable because the scene is a short platform bit.
The train is already waiting in the shot
The train, the station, and the view along the platform are part of the scene you are entering. Your portrait can be taken in a hallway, a studio, or a backyard. None of those backgrounds replace the train. The performance already includes the phone-on-train viewpoint and the run beside the carriages.
Do not upload a picture of a different vehicle and expect the scene to follow it. A bus, a car, or a toy train in the photo is not a new set. The carriages stay. If you need another location or another action, build that other idea at /video rather than forcing this platform to become something else.