Delegation Expired

I have a situation where I set delegation to a sender using code that has worked in the past.  The indication was that the delegation was successful BUT it didn't work.  Looking in the UI I figured out that the users had used delegation before and it has expired.  when I reassigned delegationI need to update the expiration date.  What should I do to fix this Remove the delegation so when I assign the new one it won't have an expiration date OR assign the delegation with a new expiration date? (I'm not sure what will work and don't see how to update the expiration date)