Partial Close is possible on Trade Interceptor Desktop and Trade Interceptor mobile.
In order to close trade partially from Trade Interceptor desktop you need to go to the Trading Control Panel (Demo Trading Control Panel or Live Trading Control Panel depending on if you are a demo or real trader with Trade Interceptor), select the "Active Trades" tab to see all your current positions and right-click on the trade you want to close partially. The context menu will show up giving you an option for "Partial Close".
In the mobile app, select the trade from Portfolio > Active Trades, and tap on the trade then select "Partial close order". After that select the amount and tap on button "Partial Close" on top.