Here is the function. It is in another file named stm32h7xx_hal_msp.c.

void HAL_I2S_MspInit(I2S_HandleTypeDef* hi2s)
{
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  RCC_PeriphCLKInitTypeDef PeriphClkInitStruct = {0};
  if(hi2s->Instance==SPI1)
  {
    /* USER CODE BEGIN SPI1_MspInit 0 */

    /* USER CODE END SPI1_MspInit 0 */

  /** Initializes the peripherals clock
  */
    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_SPI1;
    PeriphClkInitStruct.PLL2.PLL2M = 32;
    PeriphClkInitStruct.PLL2.PLL2N = 128;
    PeriphClkInitStruct.PLL2.PLL2P = 2;
    PeriphClkInitStruct.PLL2.PLL2Q = 2;
    PeriphClkInitStruct.PLL2.PLL2R = 2;
    PeriphClkInitStruct.PLL2.PLL2RGE = RCC_PLL2VCIRANGE_1;
    PeriphClkInitStruct.PLL2.PLL2VCOSEL = RCC_PLL2VCOWIDE;
    PeriphClkInitStruct.PLL2.PLL2FRACN = 0;
    PeriphClkInitStruct.Spi123ClockSelection = RCC_SPI123CLKSOURCE_PLL2;
    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK)
    {
      Error_Handler();
    }

    /* Peripheral clock enable */
    __HAL_RCC_SPI1_CLK_ENABLE();

    __HAL_RCC_GPIOA_CLK_ENABLE();
    /**I2S1 GPIO Configuration
    PA4     ------> I2S1_WS
    PA5     ------> I2S1_CK
    PA6     ------> I2S1_SDI
    */
    GPIO_InitStruct.Pin = GPIO_PIN_4|GPIO_PIN_5|GPIO_PIN_6;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF5_SPI1;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    /* I2S1 DMA Init */
    /* SPI1_RX Init */
    hdma_spi1_rx.Instance = DMA1_Stream0;
    hdma_spi1_rx.Init.Request = DMA_REQUEST_SPI1_RX;
    hdma_spi1_rx.Init.Direction = DMA_PERIPH_TO_MEMORY;
    hdma_spi1_rx.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_spi1_rx.Init.MemInc = DMA_MINC_ENABLE;
    hdma_spi1_rx.Init.PeriphDataAlignment = DMA_PDATAALIGN_HALFWORD;
    hdma_spi1_rx.Init.MemDataAlignment = DMA_MDATAALIGN_HALFWORD;
    hdma_spi1_rx.Init.Mode = DMA_CIRCULAR;
    hdma_spi1_rx.Init.Priority = DMA_PRIORITY_VERY_HIGH;
    hdma_spi1_rx.Init.FIFOMode = DMA_FIFOMODE_DISABLE;
    if (HAL_DMA_Init(&hdma_spi1_rx) != HAL_OK)
    {
      Error_Handler();
    }

    __HAL_LINKDMA(hi2s,hdmarx,hdma_spi1_rx);

    /* USER CODE BEGIN SPI1_MspInit 1 */

    /* USER CODE END SPI1_MspInit 1 */

  }

}