Delayed estate cash

I was executor for my father's estate when he died in 2016, and paid the necessary IHT. However Hargreaves Lansdown have just informed me that there is about £1000 remaining in cash which I was not aware of at the time. How do I deal with the IHT implications of this?

Hi,
Please contact the IHT helpline on 0300 123 1072.
Thank you.