Are you making a Mesh in another program, or trying to create a hat like this in Roblox Studio using Unions?
This would be difficult to make with Unions.
If you are using another program like Blender then I’d suggest looking online for tutorials to help you.
You should try a Blender tutorial instead of coming to the Roblox forum. There’s way more information out there if you just look for it.
If your hat is at 0,0,0 in Blender 2.9 you can mirror one half with the Mesh Tab tool Symmetrize. Select the half you want to mirror then it’ll come up with a menu at the bottom. You need to figure out if it’s +X to -X or any of the other selections in that small menu.
Or do you mean the odd shadows just above the brown triangle in the strap?
It looks like you have edges in your triangles that are going from convex to concave and back to convex creating those shadows.
If you look at them in Blender you can select each edge and then rotate it using the Edge tool, then go to the Edge tab and about 5 tools down there’s Rotate CW and Rotate CCW.
Try using those and viewing it in Object mode instead of Edit mode to see how those edges look.
Another thing to try in Edit mode is to select all (A) then go to your Mesh tab and select the Normals tool. Another menu pops up, choose the Reset Vectors (I think that’s the name) and this will get rid of any twists in the Mesh that may have popped up when you were moving Vertices or Edges around.