If you are hand-designing your physics, you can use Vector2's move_towards to move the object in the direction of the player as they move.
var new_prjk_pos = cur_prjk_pos.move_towards(player.position, "some int value closer");
Link to Godot Article for method
If you are using sometype of Physics engine,
var direction_toward_player = project_pos.angle_to(player_pos)
var new_acceleration_of_projectile = projectile_acceleration.rotated(direction_toward_player)
projectile_acceleration = new_acceleration_of_projectile