Kindly note that the repayment duration scheduled on the top-up cannot be adjusted. Loan Top Up is an additional loan on your running loan and it doesn't come with a separate installment as the date remains the same but the repayment value increases.
However, in a case where the interest on the Top-Up is spread across the available duration on your ongoing loan, and the interest is more than the duration, the system will generate another installment (s) which is what happened with your loan.