How to edit a table created with "Enter Data".

I'm still pretty new to PBI. I have Free PBI Desktop v2.102.845 (64 bit free version Feb 2022) on Windows 10. I use an ODBC driver to connect to a Postgresql database server.

I need to enter some fixed values into a table which will never change. The columns with sample data are like this: 

1. This table will connect the column Payrollcode to another table, so I can show ShortDesc in my actual reports.
2. This manually entered table will probably be used in many PBIX files.
3. I need to be able to name the columns "Payrollcode", "ShortDesc" and "LongDesc". 

I have entered several rows of data already via Home tab bar, and Enter Data, but I am unable to enter the rest of the codes. How do I edit this manually entered table? I have tried right-clicking the table and selecting "Edit query". I can see the rows I entered but cannot add more rows to the query. I am also unable to change the column names which are currently "Column1", "Column2", and "Column3".

Thank you!