Help required on  Demand Forecasting for Customer whose sales is decreasing

Hi experts,

My scenario is I am forecasting for 12 periods using past 12 periods data using weighted moving average.

I have a situation wherein i need to decrease the forecasted quantity by 25% for a particular customer during or after a forecasting run.

This is because currently the forecast is calculated high because of the nigh historical data and now the customer has shut down many operations resulting in low demand.

I tried with Trend dampeneing but dont know how to use it with Weighted moving average.

Need experts help and advice on this.

Thanks in advance

RR