Make sure they’re in woff2 format. Upload the font via FTP to themes/theme name/fonts/
Use https://www.fontsquirrel.com/tools/webfont-generator to convert them if they’re in another format.
@font-face{font-family:FONT NAME;font-style:normal;font-weight:400;font-display:swap;src:url(/wp-content/themes/LFWD/fonts/CHANGE THIS.woff2) format('woff2');}