Javascript to replace font across website

I need a javascript expert to create a script to replace the font on a web-based LMS I'm putting together for a client.

The LMS settings only go as far as ensuring users browsers display the font family, but I need it to display a specific font, so have to pull the font from a public server.

Font needed is Trebuchet. System is TalentLMS.

I'm open to fixed offers, please assess requirements and submit your proposal. I need this done by the end of tomorrow latest (20th) but ideally today.

Thanks.