Hi there,
Pretty sure they are on the Wiki , at the End. or sometimes on the Sales page at the bottom.
You can open them with Easy EDA and use portions for you own boards, I.e RTC section. I used it on my board and it works perfect. They even had the battery holder.
DRC version.
Expansion Board schematic files…
Seeeduino XIAO Expansion board_v1.0_200824.rar (76.1 KB)
hTH
GL 
PJ