Error warning: Unable to import presets (all iteams were already imported)

Hi guys
I'm not good at English but i hope you guys understand. I need your help.
I'm open Lightroom CC 2020 and add preset with the ways everybody did but it's not happened.
When i add presets, it shows up the message Unable to import presets (all iteams were already imported).
I tried a lot of way on internet but all failed. even change the ending text to xmp but still won't.
I tried to Delete and Download the new Lightroom but still can not working.
Hope you guys can help me. 
Thank you