This is completely safe. That tool was developed by the guys over at WavesGo and has been used by many to sort leasing problems.
That is the official link.
Thank you so much! I was asking because the first rule in crypto is don't download nothing before asking.

I made a lease some time ago and it's working great but now I want to cancel that lease.
The problem is that the lease transaction doesn't show on the Leasing Transactions list!
Is this a known problem? Any workaround?
I have the same problem, you can try the link quoted in this post. I have not tried yet.