Drag coin from debts account to wallet or to other account you have received money to. If you wish you can specify from whom you borrowed and when this debt need to be paid away.
Now the balance in wallet or other account has increased and Debt account has negative sum.
Also you can make expenses or shop in credit, with dragging coin from debt account to expense category icon.
To return the Debt open transaction list of debt account and swipe the debt transaction from right to left. Tap Return and select account you return debt from.