assignValue
creditTermRange.value = creditTermRange.value;
меняем на creditTerm.value = creditTermRange.value;
totalAmountOfCredit.innerHtml= `${lounAmount} ₽`;
totalMonthlyPayment.innerHtml= `${monthlyPaymentArounded} ₽`;
totalRecommendedIncome.innerHtml= `${monthlyPaymentArounded + ((monthlyPaymentArounded / 100) * 35)} ₽`
.innerHTML
, но я советую использовать .textContent