How to remove reference from a case

Hi,

I mentioned a number in case A with ‘Hash’ before it (’#0000xxxx’).
Since there is a GIT case B with the same number as ID (‘xxxx’), that case B took this new case A as a reference.
Even after I removed the ‘Hash’ from my new case A(‘0000xxxx’), reference from the old case B is not removed.
Please guide me on how to remove the reference from the old case B

Thanks

Gowri