"create a loop with rapidMiner"

hello,i want to use polynomial regression so as to predict the amount of products sales,whene i use it,it gives me one formula to calculate the predictive amount for all products,but the problem is that i have lot off products so logicaly it has to give me for each product his suitbale formula,so,after lot of search i found that i have to create a loop with rapidMiner that it will iterate the produts and give them the formula for each product but i don't know how to create it and make relation with products,,can you help me please?