If you want to change the sender of a campaign, please take the following steps:
go to campaigns
click on the campaign you want to change the sender of
go to the prospects by clicking on the icon in the top right corner
select all prospects of the sender in que and click remove from campaign from the right bar
After you have successfully removed the prospects from the campaign, you can add those prospects to the campaign with your preferred user. For further info, please check out this article