You want to transfer your role as Leadbuyer to one of your colleagues. To do this, go to the 'Participants' tab in the tender at hand and open the list of colleagues in your organization (click on the link 'Employees' in the third column of this page).

If you have not added any colleagues in this tender, you will a dropdown-menu at the lower left part of your screen where you can select colleagues to add to the tender.

Once the colleague that you want to transfer your Leadbuyer role to has been added to the Tender, you will see the 'Set as Leadbuyer' link right below his/her name (to become a Leadbuyer he or she will need a Negometrix license). 

Once you click this button, you immediately transfer the Leadbuyer role to the designated colleague. The colleague at hand wil not get notified. Only the new Leadbuyer (the designated colleague) or your company administrator can reverse this action.