Once you submit a time off request, you will be able to see it on the schedule, as long as you have not filtered time off requests out of view.
If you are using the mobile version of Sling, you can go to your Shifts tab, and then select either the Full schedule or My schedule tab. Then find the date for which you submitted the request, and you'll see a gray block for the request, like so:
When a time off request is still pending approval, it will be indicated on the time off block, as demonstrated below:
If you need to cancel a time off request, you can do so by tapping on the request, then tapping the 3 option dots in the upper right corner:
Note that you also have the option to delete a time off request if its status is still pending. But once a time off request has been approved, you cannot edit it, and would need to delete and create a new request instead.
If you are using the web version of Sling (https://login.getsling.com or https://app.getsling.com), then you can find your time off requests through the Schedule tab under either the Full schedule or My schedule tabs.