[Pleasing to see they still make human friendly printers].
You do it by using an "Escape code". That is, you send chr$(027) to the
printer and every character after that is interpreted by the printer as a
special 'control code' and not just as a character to print.
The codes you can send allow full control over the printer hardware and
style of printing, upto the level of controlling the individual printhead
needle patterns (pixel printing).