Well if you dont want to go through trenline route that is one solution but what tou can do is create a parameter list and then can use that value to do forecasting plus you can try inbuilt forecasting feature of tableau
Thanks for the suggestion. This will however change the historical values too. I am looking for a solution how to perform simulations for the future values keeping the historical values as is.
Try Please Nothing is going to go wrong. You can Try Trendline Route. Get the most Significant Model ,.There are many there and then use that for Forecasting.