You can negotiate with Xiao Zhang to find out why he doesn't pay it back, whether there is a repayment plan, etc. If Xiao Zhang is willing to repay, he can agree on a repayment plan and sign a written agreement to ensure the safety and rights of repayment.
3. If both parties can't reach an agreement, they can apply to relevant institutions for mediation. Mediation agencies can coordinate the two sides to reach a settlement and reduce the occurrence of disputes.