You may want to give these a read / watch:
http://4cardata.info/elearn/199/2/199000000/199000005/199000001/199000607
https://www.youtube.com/watch?v=6Z0CaujMuN0&list=PLg8oXPEYKmMT4RiB_mRr9jm5kehYPghmR&index=15 - This is in italian and its for a timing belt change, but you see how they refit the drive belt. If you youtube search timing belt changes for grande punto's and fiat puntos , as removing the aux belt is part of the process you may get a better understanding of removing tensioner.
https://www.youtube.com/watch?v=Xv_4tKhoOQ0 - My video explaining some things. Apologies for length wasnt sure if u need auxbelt and tensioner removal explanation.
Hope it helps. If you need more help i just remembered I still have my older tensioner so can do a video of how it works out the car, but currently just going into work so will have to be tomorrow now.