Board Thread:The Quarters (Q & A)/@comment-68.227.229.21-20140128222030/@comment-24185151-20140211105513

You can restore your streak (if you remember the number) by clicking on the advanced section whilst editing your tasks. :) I hope that helps.

Unfortunately there is no way to "undo" a broken streak as I don't think HabitRPG keeps that data once it's been removed. However, you could request this on the HabitRPG trello as a future feature.