I know it’s been old, but if you are still looking for the solution, the below thing will help you as I tried it on my work.
the Left, right and centre functions consist of the code you used already.
When the player wants to switch the lane, I just get the input left/right and set it to the level Manager( according to my project). If you want you can cast to the game mode and get it in the floor tile bp. Hope this will solve your issue but for the smooth transition, I can’t help as I am still figuring it out. Maybe if I got a solution will definitely update it here.
Cheers.