There isn't a way to change the status to expired. But the Background Check dashboard will show you backgrounds checks that have expired so you can order a new one. Please add the request to set status to expired in the Ideas for Ministry forum. 

@Beau Dansizen5 There is not a way for volunteers to currently self-schedule. What they are able to do is if, for example, I were a volunteer already scheduled and can no longer serve for an upcoming time, I am able to find a replacement volunteer and someone else can respond to that notification to take the slot for me. I can also accept or deny assignments.

I believe you will find a request for this in Ideas for Ministry for self-scheduling, so please vote on the request.