how to use sd_flash_write? SDK13

I want to write at the end of memory ROM data in address 0x7FFFF

uint8_t tst_arr[1] = {6};
sd_flash_write((uint32_t*)0x7FFFF, (uint32_t*) &tst_arr, 1);

Is it correct?

But if I made it, in a memory watch I can't see any changes from 0xFF to my data (6).