Download Nier CLI. This program is used to convert .wtb texture files to a standard viewable image format, or into .wtb.
Create a new folder named <YOUR_FILE_NAME>.wtb_extracted. <YOUR_FILE_NAME> should be replaced with the output texture file name you want. The .wtb_extracted at the end of the folder is important.
Create and/or add one or multiple .dds files to the folder.
Drag the folder into the Nier CLI executable. This will overwrite any .wtb file if any already exists with the same name.