MicroMod SAMD51 Processor Board Hookup Guide
bboyho, 
Elias The Sparkiest 
Setting Up the Arduino IDE
Install Arduino SAMD Board Add-Ons
First, you'll need to install a variety of tools, including low-level ARM Cortex libraries full of generic code, arm-gcc to compile your code, and bossa to upload over the bootloader. These tools come packaged along with Arduino's SAMD board definitions for the Arduino Zero.
To install the Arduino SAMD board definitions, navigate to your board manager (Tools > Board > Boards Manager...), then find an entry for Arduino SAMD Boards (32-bits ARM Cortex-M0+) by typing SAMD in the search bar. Select it, and install the latest version (at the time of writing this tutorial, the board definitions work with v1.8.9).
Downloading and installing the tools may take a couple minutes -- arm-gcc in particular will take the longest, it's about 250MB unpacked.
Once installed, Arduino-blue "Installed" text should appear next to the SAMD boards list entry.
Install SparkFun Board Add-On
Now that your ARM tools are installed, one last bit of setup is required to add support for the SparkFun SAMD boards. First, open your Arduino preferences (File > Preferences). Then find the Additional Board Manager URLs text box, and paste the below link in:
language:bash
https://raw.githubusercontent.com/sparkfun/Arduino_Boards/main/IDE_Board_Manager/package_sparkfun_index.json
Then hit "OK", and travel back to the Board Manager menu. You should (but probably won't) be able to find a new entry for SparkFun SAMD Boards. If you don't see it, close the board manager and open it again. ¯\_(ツ)_/¯.
This installation should be much faster; you've already done the heavy lifting in the previous section. When writing this tutorial, the board version used in this tutorial should be v1.7.6. You may have a higher version as the board if there are any updates.
Select the Board and Serial Port
Once the board is installed, you should see a new entry in your Tools > Board list. Select your SparkFun MicroMod SAMD51.
Finally, select the SparkFun MicroMod SAMD51's port when the board is connected to your computer. Navigate back up to the Tool > Port menu. The port menu will have the SparkFun MicroMod SAMD51's port, labeled as such here. On a Windows machine, the serial port should come in the form of "COM#". On a Mac or Linux machine, the port will look like "/dev/cu.usbmodem####".
In the picture above my MicroMod SAMD51 is listed under COM25; this is because I've plugged in about as many microcontrollers into my computer, but the one in your port menu should be smaller.