Uninstall WAIK8.1 from SCCM server now, , reboot and then install WADK10.
You can download WADK10 from the link below
Update the Boot Images:
Open the SCCM Console Go to Software Library / Operating Systems / Boot Images
Select your boot image, right-click and select Update Distribution Points Repeat the steps for all your boot images
This will replace the boot image and use the new boot image from ADK.
On SCCM Console Navigate to Administration / Site Configuration / Sites
Click the Hierarchy Settings in the top ribbon Select Automatic Client Upgrade tab
Enable the option “Upgrade client automatically when the new client update are available”
Create a folder named UserStateMigrationTool under your SCCM source directory. I created it under W:\Sources\OSResources\.
Navigate to C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\User State Migration Tool and copy all files and folder from here to W:\Sources\OSResources\UserStateMigrationTool .
Navigate to Software Library / Application Management / Packages
Under Packages modify the User State Migration Tool source folder from C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\User State Migration Tool
to the UNC path \\sccmserver\Sources\OSResources\UserStateMigrationTool
Also change the package name to Win10
distribute USMT to the DP
The default boot images should be updated to WinPE 10 (10.0.10240.16384)