Here you will find the Windows 10 driver for the ASUS USB-BT400 Broadcom Bluetooth adapter. The driver is version 188.8.131.529 and was released in November 2015. You can download the driver below.
Note that this driver comes in a .cab file and you will need to download and extract the .cab file from the zip file. Once you have extracted the .cab file remember where you had extracted the file contents too. You will now have to open your control panel. This is done by opening the Device Manager (right click on My Computer, choose Manage and then find Device Manager in the left panel. Right Click on the device you wish to update. Then click update software and browse to where you had extracted the file contents.
If you are looking for the Broadcom Jungo driver then see here.