Once you have your account structure setup in SAP BTP Cockpit, navigate to Global-account → Sub-account → Space. Afterwards click on SAP HANA Cloud from the menu on the left side of the screen.
For the candidate SAP HANA Cloud instance, navigate to Actions → Open in SAP HANA Cloud Central.
A new tab will be opened for SAP HANA Cloud Central Cockpit and your list of instances will be displayed for a selected space. From Actions column, click on the 3 dotted icon.
Select Delete option from the menu.
It will ask for re-confirmation and type DELETE into the text box, then press the Delete button.