Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Keil/AT32F415xx_v2/IOMUX/REMAP6#0x0
IO MUX remap register 6
CAN1 muxing
SDIO1 muxing
USART1 muxing
USART3 muxing
UART4 muxing
https://github.com/cmsis-svd/cmsis-svd-data