Blender 3d model -Help to fix exporting issue

I received a 3d model of a boy in blender from developer and decided to make a girl by myself. I am a blender newbie. But I must have clicked something wrong that my model became looking flat, with no shadows. I still was able to import her into unreal and I received a very wrong model, compared to the one I worked with.

I suspect that I just need to click a few buttons to return to the mode that will do right export settings. I need help - please tell me what to do?

In the attached images - first - this is how she looked in blender.
Then how she looked in unreal engine (with new materials)
Third - comaring the boy model - right one and the girl - wrong one.
Help me to figure out what to ckick on blender so that I could return to the right settings to create a right fbx file!

Hi,
I am also fairly new.
But you could try recalculate the normals
select the mesh in object mode and press CTRL+N

It reloaded a start up file, and my object disappeared. No, didn’t work.

The issue is resolved. The editor was in modification mode, close it to normal.