First send it to the desert empire woodland, then click on the small map in the upper right corner to open the map details and come to the river under the wooden bridge outside Palau. Then carefully observe the coordinates of the small map and slowly move to coordinates 270,245, and then you can find the third stone tablet in the river.

Introduction to the location of the third historical stone tablet

First, open the world map and send it to the desert empire woodland.

Then continue to open the map and come to the river under the wooden bridge outside Palau, as shown in the red circle below.

After coming to the said position, notice that the coordinates of the small map continue to move to 270,245, and you can see the third stone tablet.