This is an old post now, but still holds true. The only thing to remember is that the app might not be called XBMC, so look for:

Kodi (or Kodi 4 DroidBOX)
DBMC
XBMC (or XBMC 4 DroidBOX)
SPMC (or SPMC 4 DroidBOX)

when scanning down the list of apps.

To reset your app’s settings to their original defaults, please do the following.

Note that this will wipe out ALL customizations you have made since first using Kodi/DBMC/etc, and any downloaded metadata (album covers, film posters, artist info etc) caused by importing your media collection will have to be redownloaded.

Start from the Android homescreen, and bring up the list of all installed applications (normally a circle with six dots, or a “My Apps” icon).

Select Settings, and click on Apps (if you can’t see an entry for Apps, please click on the OTHER tab and select the More Settings button). Wait for the list to show.

You may need to scroll, but you should see an entry for Kodi (or the names above) – click on it. If it is not greyed out, click the button labelled Force Stop and confirm you’re certain. Now click on the Clear Data button please and once again confirm. Wait until the statistics for space taken have updated, and return to Android’s homescreen.

Lollipop Devices:

DroidBOX® T8-S Plus Settings Clicked
Kitkat Amlogic Devices:

DroidBOX® T8 Settings Other Tab
Older Devices:

DroidBOX® X7 Settings