I need blink my led in "distress signal" Urgent please

I have a Nucleo-32 STM 432, ARM Cortex M4 and my teacher asked us for a program in which the pin turns on and off simulating a "distress signal" (SOS) in Morse code (... _ _ _...). This is my program, but I don't know how to configure it so that my led blinks in this way. I hope you can help me.

;*******************************************************************************

DELAY_INTERVAL EQU 0x124F80
;**************************

;STM32L43xxx reference manual RM0394, p.64
RCC_AHB2ENR EQU 0x4002104C ;Clock control for AHB2 p.214-215

;GPIO-B control registers
GPIOB_MODER EQU 0x48000400 ;set GPIO pin mode as Input/Output/Analog
GPIOB_OTYPER EQU 0x48000404 ;Set GPIO pin type as push-pull or open drain
GPIOB_OSPEEDR EQU 0x48000408 ;Set GPIO pin switching speed
GPIOB_PUPDR EQU 0x4800040C ;Set GPIO pin pull-up/pull-down
GPIOB_ODR EQU 0x48000414 ;GPIO pin output data
;***************************

AREA MyCodigo, CODE, READONLY
ENTRY ; Mark first instruction to execute
EXPORT __main

__main
; Enable GPIO clock
LDR R1, =RCC_AHB2ENR ;Pseudo-load address in R1
LDR R0, [R1] ;Copy contents at address in R1 to R0
ORR R0, #0x00000002 ;Bitwise OR entire word in R0, result in R0
STR R0, [R1] ;Store R0 contents to address in R1

; Set mode as output p.263
LDR R1, =GPIOB_MODER ;Two bits per pin so bits 0 to 3 control pins 0 to 3
LDR R0, [R1]
ORR R0, #0x00000055 ;Mode bits set to '01' makes the pin mode as output
AND R0, #0xFFFFFF55 ;OR and AND both operations for 2 bits
STR R0, [R1]

; Set type as push-pull (Default)
LDR R1, =GPIOB_OTYPER ;Type bit '0' configures pin for push-pull
LDR R0, [R1]
AND R0, #0xFFFFFFF0
STR R0, [R1]

; Set Speed slow
LDR R1, =GPIOB_OSPEEDR ;Two bits per pin so bits 0 to 3 control pins 0 to 3
LDR R0, [R1]
AND R0, #0xFFFFFF10 ;Speed bits set to '00' configures pin for slow speed
STR R0, [R1]

; Set pull-up
LDR R1, =GPIOB_PUPDR ;Two bits per pin so bits 0 to 3 control pins 0 to 3
LDR R0, [R1]
AND R0, #0xFFFFFF10 ;Clear bits to disable pullup/pulldown
STR R0, [R1]
;***************************
turnON
; Set output high
LDR R1, =GPIOB_ODR
LDR R0, [R1]
ORR R0, #0x0000000F
STR R0, [R1]
BL delay ; Call subroutine delay
turnOFF
; Set output low
LDR R1, =GPIOB_ODR
LDR R0, [R1]
AND R0, #0xFFFFFFF0
STR R0, [R1]
BL delay ; Call subroutine delay
; loop
B turnON

; Subrutina delay
delay
LDR R2,=DELAY_INTERVAL
ret
CBZ R2, delayDone
SUBS R2, R2, #1
B ret
delayDone
MOV pc,lr ; Return

END