Yes, you can download the source code of a Swift app from GitHub or other sources. However, you might encounter an issue with the Swift version. The article provides guidance on how to change the Swift version of the app. But, don't forget that there are instances where code refactoring is also necessary.

To change the Swift version in Xcode, follow these steps:

Open your Xcode Project:
Launch Xcode and open the project for which you want to change the Swift version.

Select the Target:
In the project navigator on the left-hand side, select the project's target for which you want to change the Swift version. This could be your main app target or any framework target within your project.

Change Swift Language Version:
With the target selected, go to the "Build Settings" tab. You can find this tab by selecting your target, then clicking on your project name at the top, and finally selecting the "Build Settings" tab.

Search for "Swift Language Version":
In the search bar of the "Build Settings" tab, type "Swift Language Version". This will filter the settings to show only those related to Swift.

Choose Swift Version:
You will see an option named "Swift Language Version". Click on it and a dropdown will appear. You can select the Swift version you want to use from the available options. The options might include versions like "Swift 5.0", "Swift 5.1", "Swift 5.2", etc., depending on your Xcode version.

Clean and Rebuild:
After you've changed the Swift version, it's a good idea to clean your project and rebuild it to ensure that any dependencies or code changes are compiled correctly with the new Swift version.

Test your App:
Thoroughly test your app to make sure that it works correctly with the chosen Swift version. Sometimes, changes in Swift versions can introduce compatibility issues.

Remember that changing the Swift version might require you to update parts of your code to match the syntax and features of the chosen Swift version. Some newer Swift versions might introduce breaking changes or deprecated features, so be prepared to make necessary adjustments to your codebase.

Additionally, be aware that not all Swift versions might be available in all versions of Xcode. Newer versions of Xcode tend to support the latest Swift versions, so make sure you have an appropriate version of Xcode installed if you want to use a specific Swift version.