On the graphical viewer I’ve clicked “Download”, then downloaded the FASTA of the whole thing. The file is called “GU305914.1[1..230408].fa” The IGV website says that I can load my own genome if I have the FASTA file:
Did you click “Send to” and then select “File” from this page? If you do that then that should save it as a plain text fasta file. I suggest that you download the IGV local app for your OS and then follow the directions you linked above for LoadGenome. Necessary index for the fasta file is automatically created in that case.