Windows 10 preview build 20190 lets users decide which graphics card should be set as the default high-performance card. Windows 10 will soon also allow users to specify on a per-application basis what specific GPU you want to use with an application. Users can install the latest Windows Insider build of the latest version of the Windows 10 software. The feature is expected to be released in a feature update in the near future, but users will need to wait until it is released in feature update. The latest build of Windows 10 is 20190.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-to-give-power-users-more-control-over-their-gpus/