Async Await in F#

I am rewriting some of the C# in this lab to F#: https://github.com/Microsoft/TechnicalCommunityContent/tree/master/IoT/Azure%20Stream%20Analytics/Session%202%20-%20Hands%20On

I am on Exercise 6, #17 - creating the SimpleEventProcessor type.
I want to implement the CloseAsync method

C#

async Task IEventProcessor.CloseAsync(PartitionContext context, CloseReason reason)
    {
        Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason);
        if (reason == CloseReason.Shutdown)
        {
            await context.CheckpointAsync();
        }
    }

and I started like this:

member this.CloseAsync(context, reason) = 
    Debug.WriteLine("Processor Shutting Down. Partition '{0}', Reason: '{1}'.", context.Lease.PartitionId, reason)
    match reason with 
    | CloseReason.Shutdown -> await context.CheckpointAsync()
    | _ -> ()

but I have 2 questions:

1. How do I return await in F# world?
2. How do I return the NOT case -> C# just ignore that possibility.