You said you understood modelling and UV mapping.
You need to cut the geometry. There are lots of ways to do that in 3dsmax such as using the ‘cut’ tool which offets the ‘plane’ where you can use the selected viewport (ie top) as the plane and you set the depth. Then you set a different material ID on those cut polys.
if you meant the other comment, you use the texture coordinate node in UE4 and set tiling to greater than 1. Then you hand paint a black and white mask to blend in your other texture. Its up to you to make it match.