Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/stm32/stm32wl/STM32WL5x_CM0P/TIM2/TIM2_AF1#0x0
TIM2 alternate function option register 1
External trigger source selection
https://github.com/modm-io/cmsis-svd-stm32