read/write file was changed to read only how do I change it to read/write againt

Loading libreOffice took much longer than usual. I started to input new data in the cells which contained previous data and everything seemed to be working correctly.

I started to enter data into a row of cells that were formatted to print size of 15 with BOLD as a setting, I started to enter data and changed the print size to 10.5 and disabled BOLD setting.After this change I was no longer able enter new data or change old data.

I tired to copy data to a new file but it would not copy: read only file.

How do I get the file to be read/write again.