Hello,
I have a question about STM32F407.
I was wondering how to software trigger (not external trigger) a "one 
pulse" timer, using HAL library?
Thanks for the help.

I don't know if there is a special HAL way to do this.
But why not setting the corresponding bit in one of the "interrupt set 
pending register" NVIC_ISPR0 through NVIC_ISPR7?

See:
 Cortex M4 M4 Devices Generic User Guide 
https://developer.arm.com/documentation/dui0553/a/
"4.2.4 Interrupt Set-pending Registers"

There should also be a CMSIS function NVIC_SetPendingIRQ(IRQn_Type 
IRQn), see "4.2.1 Accessing the Cortex M4 NVIC registers using CMSIS"

After setting the bit I expect the IRQ to run (if enabled and no higher 
prio interrupt running).