Who owns the account?
As an individual you cannot report anything to the credit bureaus. How did the debt got there in the first place? Surely you didn’t report it to the credit bureaus yourself?
My guess is that your former tenant debt went to collection, and it’s the collection company that reported it.
Under what name your former tenant debt is reported? This is the entity that owns the debt, and he should do all negotiations with them.
In any case, even is he pays I doubt if they will remove it from his report, and it won’t raise his credit score.
See why-pay-off-debts.html and how-to-pay-off-debt.html for a more detailed explanation.