Typically, a command box should appear on screen, asking for the name of the file to be saved. Use the original file name as programmed, but the tagname (last three characters after the period) would by default be "bin" (for binary). Use another tag name, as previously noted.. to ensure the old file being saved does not overwrite the newer file.
With modern BIOS programming, the program file may exceed 2 megs.. so a floppy disk would not be appropriate. Hence the trend toward a USB flash device. The link evasive provided is well heeded!
When in BASIC mode of operation, you have only a 16-bit platform of use.. hence only 8 characters for a file name, plus allowable three characters for a tagname. Each character requires two bits of information!! Refer to the ASCII table.
F@H.. to solve mankind's maladies.. in our lifetimes!