The RTC in my chip isn't really accurate. I think I'm not the only one

I looked in the library source code, but didn't find any existing function that allows correcting the clock.

I think it would be very important to add a function to correct the clock. This can be done using the FREQCORR" register.

Datasheet:

https://cdn.sparkfun.com/datasheets/Dev/Arduino/Boards/Atmel-42181-SAM-D21_Datasheet.pdf

Register in the page 262.