Cancelling your open orders on Arihant Plus is very simple.

Click on Trades in the bottom panel

You will enter the holdings screen by default, switch to "My orders" to check your order history.

Here you can see all your orders or choose to see only your open or closed orders. 

Find the order you want to cancel, clicking on the order will give you options to modify / cancel the order

You can also create a custom view of your order book by clicking on the filter button. You can understand more about creating your custom view here.