Creating iOS Asset Catalogs Manually with Xcode
To create iOS asset catalogs with Xcode
1. Launch Xcode.
2. Select File > New > File... from the menu at the top of the screen.
3. Select the iOS filter at the top of the screen, then scroll to the Resources section, and select Asset Catalog.
4. Click Next and specify where to save your asset catalog.
5. To add a new image to the catalog, right-click the left-hand pane of the screen, and select New Image Set. A new section opens in the right-hand pane for this new image set.
6. Double-click the image name and specify a new image name.
7. If you require more icon categories, right-click the Image set, and select iPhone or iPad.