To reverse the direction of a model train you can use two main options.
This video link shows is the simplest option and least expensive option. Watch the video and it saves me drawing.
You need two points or turnouts, here we use two RH ones.
Both are connected to the main loop. The top points accepts the train coming in clockwise direction. Our aim is to get the train to come out traversing counterclockwise. Thus the points need to be set, firstly to take the train off and then to allow the train to move back onto the main track.
Both points are connected with a separate track, its length and shape depends on dimensions of your layout.
This section of track needs to be isolated with its own power. I have placed the isolation sections at the end of each point to the connecting track.
The polarity of this isolated track will match that of the incoming train.
As the train enters the isolated section you need to switch the polarity of the outer track in this video to counterclockwise wise. The train will then travers the point and move back onto the outer track in the opposite direction.