If your Schedule Mode is "Critical Chain", do not forget to select the Planning Mode. The Switch to Tracking Mode () button must be displayed in the Main toolbar.
Log in to the HTML5 client.
Select the Work workspace, Gantt tab.
Select a project in the Project Data Selector.
Select the Scheduler () mode.
Hold down the Shift key while hovering the mouse pointer on the task bar to access the Split task icon.
Then, place the Split task icon where the task is to be split and hold down the left mouse button to drag the split part of the task to the desired amount of time.