You can cancel requests for items that have yet to be approved by following the below steps.
Cancel pending requests
Navigate to the My Tasks App portal for your organization.
In My Tasks, select My Requests and enter any relevant search text into the search field to filter your requests as needed.
Click the Pending Item button for the pending request you want to cancel.
From the Overview tab of the card that appears for the pending item, click the Cancel Request button.
Click the Confirm button.
You should see the status of the request update to show that it has been canceled.