Are you looking at some old documentation or something?
Choose a texture, click on it, the texture importer inspector will show, then change the dropdown to say advanced and then choose the format you want, then hit Apply.
Thank you sir! I found out the setting of texture importer.
And I have written sour code of asset importer but I don’t understand where to place this.
I wanted to add to MainCamera as cobut I couldn’t do that.
I placed MyAssetImporter under Editor direcotry when onPreprocessTexture() called assetImporter is null and unity did hang-up.
So meanwhile, I pass over to use MyAssetImporter.