How do i fix a split screen of my Toshiba c600d-t36b laptop

Hyjackers ,
so you HyJaCKED, A VAGUE USELESS POST.
How nifty.?
OP never told what split means
My wild guess, it is CRACKED screen
as on phyiscaly cracked
no photos of damage so any blind assessment is silly
to a fault.
sorry but on might guess, new screen time.
buy one install it.
or get a shop do do this, as 99% would do. (wise)

The quickest way to change the display output settings is to use the
display hot key (Fn + F5):
1 Press Fn and F5 simultaneously.
2 While holding down Fn, press F5 repeatedly until the setting
you want takes effect. Briefly pause each time you press the F5
key to allow time for the display to change.
This hot key cycles through the settings in the following order
(the last two options are available if an external monitor is
connected):
? Built-in display only
? Built-in display and external monitor (simultaneously)
? External monitor only
? Built-in display and TV (or other external video device)
? TV (or other external video device)
? External monitor and TV
? Built-in display and external monitor (extended mode)
? Built-in display and TV (extended mode)
? External monitor and TV (extended mode)
? Swap-Switch primary display between internal display
and external monitor when using extended desktop