Disk is locked.... While updating my mac to catalina

[7Ryanjlee-korea]

I am trying to upgrade my old mac to new version. So i started with upgrading macbook pro mid 2010 to catalina. When i open the patcher and go on the steps, there are steps which contains a messsage to choose disk. When i click one it says disk is locked, and the other says cannot install. I don't know what to do.
Here is a link for what program im using : https://www.ifixit.com/Guide/How+to+Install+macOS+Catalina+on+Unsupported+Macs/136066
https://dosdude1.com/catalina/