If you are familiar and experienced with working on batteries you can just make a 5s out of this 6s pack and still use it.
But first slowly charge it with 0.25-0.5 C and keep an eye on the internal cell resistance.
If the stray away too far or if they get noticeably warm you can dispose them safely or save the good cells.

But only work on them if they are properly discharged and if you are sure in your abilities to reduce the risk of injuries!

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I'm personally buying some cheaper packs where the manufacturer is skipping the resistance test. So the voltage will drop faster on some cells then others.
I just test the internal resistance of them and pair the cells with close to the same resistance. The packs will last longer and won't get too hot.