How can one repent from the sin of seizing Zakat and charity funds designated for the poor, knowing that the amount is large and cannot be returned in one lump sum, and will repentance be accepted with repayment in installments?

We ask Allah to accept your repentance and rectify your affairs. Do not despair of His mercy. If you are unable to pay immediately, then pay as soon as possible and fear Allah to the best of your ability. Resolve to pay as soon as you are able. It is not permissible for you to delay or pay in installments if immediate payment is possible.