How to set more UART, SPI and I2C on a customed design based on mkr wifi 1010?

Hi, I've downloaded variant folder for mkr wifi 1010 board (seems like I have to set something in "variant.cpp") and not sure How to set up SERCOM ports in order to use more than one of UART, SPI and I2C on my customed design pcb arduino based on mkr wifi 1010 board. Thought SAMD21 got 6 SERCOMs in total. FYI, I got ATMEL ICE debugger at home. Thanks for your help!

Thought SAMD21 got 6 SERCOMs in total.

The default variants seem to use 5 of them: 2 UARTs (Sercom4, Sercom5) 1 user SPI (Sercom1) 1 SPI for WiFi module (Sercom2) 1 I2C (Sercom0) I guess that leaves Sercom3. It looks like all 4 pins are available on Pins D0,D1,D6, and D7...

Thanks! for your reply.. and How can I know the syntax of 'variant.cpp' in order to re-write my own version ? (seems like c++ ) not really sure which book or guideline to read? any suggestions please?