Hi,
For this you need to create a custom module and add the fonts and scss. Let us walk you through the process.
Here, A new module is created and it's named custom_font. Don't forget to add the __init__.py file and manifest.py file.

Inside the static -> src -> create 2 folders named fonts and scss to load the fonts and scss.
Go to https://fonts.google.com/specimen/Poppins this link and download all the poppins fonts.
Copy that to the fonts folder.

Next you need to create an scss file.
Here,
it is named custom_font.scss and you have to load the font file that
you want to use in font-face and give font-family to the elements you
want it to be applied to.

Next you need to mention the scss file in the report asset bundle in the manifest file.

That's all for development.
Add the module in the addons directory and install it and all the reports will be poppins.

Hope it helps