Disclaimer: I am not affiliated with the creation and distribution of any of the files linked below, therefore i cant confirm their safety, proceed with caution.

To start, i recommend downloading an ad-blocker so you dont click on any fake download links (this is where getting a virus is the easiest!!!). The most popular and recommended is uBlock origin along with the firefox browser.
https://ublockorigin.com/
(this will come in handy in general internet usage so dont skip it!!!)

First, download an emulator. This will read the game file and act like a switch. I've found this release of ryujinx works well:
https://git.ryujinx.app/ryubing/canary/-/releases/1.3.265
(select the appropriate version for the device you have)

Then you download the prod keys and firmware. These are nintendos copyright protection, without them the game will refuse to open.
https://prodkeys.net/ryujinx-firmware-v3/
https://prodkeys.net/ryujinx-prod-keys-n28/
(i recommend the latest version as its the onely one ive tested)

Last but not least, get the game file
https://nswpedia.com/nintendo-switch-roms/simulation/tomodachi-life-living-the-dream

Now to set everything up:
Extract "ryujinx-canary(...)" to a folder and run "ryujinx.exe" (found inside of the "publish" folder)
Now extract the prod keys
Now that youve got ryujinx open click on "actions" then "install keys (folder)" then select the prod keys folder
Next is the firmware, click "actions", "install firmware (zip)" and select the firmware zip

Your emulator is now set up to run any game!!!!!

To load the tomodachi demo click on "file", "load application" and select the .nsp file of tomodachi life

bonus tip:
if youre playing on pc with your keyboard you'll want to rebind the "A" button to something like "pg up" so you dont turn off the text box while typing the letter "z"
To do this click on "options", "settings" and "input" then under "buttons" category click the "z" (which in default is corespondant to the "a" button on switch) and press the "pg up" button on your keyboard
Now take a screenshot of the controls and keep it to the side of your game window, that way when the game prompts you to press a button, you will know which one to press. After a while you will get used to the controls and be able to play without it

If everything went well you should be done and ready to play!!
If any issues pop up let me know!!!