2015 Trophy

Hi everyone
Thanks for letting me join. A friend of mine has a 2015 trophy se which he is unable to use at present and as asked me to ride it from time to time to keep everything moving and lubricated.
I rode it for the first time this week and found it was like being on a boat, the rear suspension seems to have failed. Every bump you go over the rear end just bounces up and down, its not solid ie tyre doesn't leave the road. If you put it on the main stand and put weight on the back end and let go it will bonce about 3 times before coming to rest. I'm not sure how you adjust the suspension on this bike but I'm pretty sure even on the softest setting it should not do this. Looking for advise of how to cure this I'm assuming the rear shock had failed so looking to replace it or get it rebuilt. Any ideas? Does anyone have one for sale?
Regards keith