You are not able to find the reset button under Live Activity Center in RUI.
SAP CLOUD FOR CUSTOMER 1802 / 02
The reset functionality, same as there is in HTML5 to clear off the Live Activity, is currently not available in RUI.
This functionality is planned to be made available in a higher release. At this point in time, we are not in a position to provide more accurate information on date and/or timelines for this future release.
Reset; RUI; Button; Call; Live Activity Center; , KBA , LOD-CRM-LA , Live Activity , How To