This is interesting.
I tried setting up Rocket Chat and messed something up in the settings and now it's basically locked me out 100%, I have zero ability to change anything and (using Una Hosted) I tried to uninstall and reinstall, and it made no change.
When you reinstall Rocket.Chat, you need to drop old database, or use new one, then you will be able to use Chat from the scratch. If you are using these instructions to install Chat then you need to modify the following line to run Chat on new Database:
Which will leave the old database on the server. Of course you need shell access to run the mongo shell; which you don't get with the critically limited Cloud hosting; [edited by AlexT]. If as the OP said, using UNA hosting then you need to contact Boonex to fix the problem since you can edit any files as outlined in this solution.