The adjustment sales rep used for giving the contribution percentages above 100% for the sales rep. Enable the adjustment sales rep feature go to Setup>Sales>Sales Preference
Tick the allow over the assignment in the sales teams check box.
At the bottom of the page add the name for the Adjustment rep.
In the sales role filed select Adjustment rep ( to add an adjustment rep to a sales team open the sales team group record at setup>sales>sales management >sales team. On the member subtab select the adjustment rep)
In the customer record, we can set contribution as 100% for both of our sales reps using the adjustment sales rep.