Welcome to my starter guide to filling in warps, now warps are usually plastic that have sunk in the surface so my recommended approach is to fill it in with a decent amount of putty. Tamiya's Basic Putty is my go-to guy when it comes to getting rid of these warps. So lets begin.

This fresh tube can last years if used for the right purposes. 

This one lasted 3 years till it dried up eventually.

The putty may be applied with a hobby knife but i choose to use a toothpick since it makes things easier for me and i get to spread it quite accurately.

Apply the putty and be sure to cover up the surface where the warps are located. Its important to be able to completely fill up the warped plastic. Excess putty is fine, it can always be sanded down after.

Here's a few examples after covering warped pieces.

It can also be used to fix molding flaws.

I sanded the parts down starting with a file, then worked my way down to lower grits of sandpaper. The good thing about Tamiya's putty is that when scratched with abrasives it releases a metallic sheen to indicate whether or not it has been touched by the sandpaper. This gets useful when filling in warps, because with it you can tell if the surface has been equally smoothened. 

If you look closer there are still areas in the putty that wasn't completely filled in, a second application would be needed.