https://sims4studio.com/thread/258/start-finish-accessory-mesh-beginners
Parts I-V are here: Sims 4 Studio - Start to Finish New Accessory Mesh for Beginners I-V
Part VI: Importing Mesh & Adding Textures
Now that your mesh is complete you can import it into the .package to view on the model there. Following that we will create a new texture for the mesh, import it into the .package, and then create a second swatch choice for players to select in the game.
- Open Sims 4 Studio and select My Projects. A navigation box will pop up. Use that to navigate to your project folder and select your accessory.package

- Click the Meshes tab.

- Click the Import Mesh button.

- Note: initially the model will display your mesh with EA's texture still there because you have not imported anything to replace it with yet.*

- Click the Swatch and Texture tab.

- Click the Export Texture button.

- *A navigation box will pop up. Enter the name you want to use for the image and save it. A new box will pop up. This is the folder that you saved the image in. If you have created a file
association for .dds with your 2D editor you can just click on the .dds and it will open. Otherwise, close the popup and open the image from your 2D editor. This tutorial will show how to
- Once your image is open in your editor choose the rectangle select icon.