How the United States could block WeChat and TikTok from Americans

One of the ways the United States could block access to WeChat and TikTok is to order smartphone software giants Apple Inc and Alphabet Inc's Google to remove the apps from their app stores. — Reuters

President Donald Trump has threatened to ban the short-video app TikTok and messaging service WeChat by late September on grounds that the Chinese-owned apps pose a national security threat. It would mark the first time the United States has attempted to shut down widely used mobile Internet apps.

How would the United States go about blocking access to TikTok and WeChat?