First things first.
What are you using to try to import this map?
I use L3DT. Use to have videos up on tiled terrain but I have removed them.
You need to make it a r16 heightfield and size it to the UE standard. Here are some wiki pages to get you started.
https://wiki.unrealengine.com/Landscape_-_Sizes_and_Height_Guide
https://wiki.unrealengine.com/World_Machine_to_UE4_using_World_Composition