End of life planning of existing products with new products Introduction

Summary:

How can we perform the end of life planning with the new the products introduction

Content (please ensure you mask any confidential information):

We have the option to copy the similar item's history and generate the forecast for the new products, but if the new product is taking some share of the existing product, how can we decrease the forecast for existing product

EX: ITEM02 lauched with NPI functionality and copied the history of similar item ITEM01, But due to the lauch of ITEM02 the demand for ITEM01 will be reduced by 40%, in this case how do we reduce the forecast of ITEM02 by 40%.