I used the Power BI Pro trial to check out report sharing. After the Pro trial ended I no longer have access to view or change permissions to the reports although they can still be viewed by others who still have access to Pro. Can I change the permissions on the reports other than deleting them? This appears to be a security issue. It would make sense if I could remove people, but not add them. It doesn't make sense that others can view my reports when I no longer control the permissions for sharing.
After posting this in the Server community, I received an email welcoming me to a Power BI Pro 60 day trial. When I clicked on the link, I had to log in to Power BI as if it were my first time logging in, but my account showed up the same without Pro access. I have already used the Pro trial and the free extension. I requested having Pro added as an enterprise license, but that hasn't happened. If I could pay for Pro access myself, I (and my team) would until an enterprise license is available, but I can't pay for Pro access myself either.
As it's free license, I'm afraid it's not able to change sharing settings for dashboards and reports. If you have backed up pbix files or you are able to download report from Power BI service, you can delete reports then republish them.
We can purchase Power BI Pro through Microsoft Office 365 or through a certified Microsoft partner, see: https://docs.microsoft.com/en-us/power-bi/service-admin-purchasing-power-bi-pro
I would suggest you post a idea here: https://ideas.powerbi.com/forums/265200-power-bi-ideas