Given a load of fonts:
iosevka-bolditalic.ttf
iosevka-boldoblique.ttf
iosevka-bold.ttf
iosevka-extrabolditalic.ttf
iosevka-extraboldoblique.ttf
iosevka-extrabold.ttf
iosevka-extralightitalic.ttf
iosevka-extralightoblique.ttf
Move them to the user font directory:
mv *.ttf ~/.local/share/fonts,
Update the font cache:
fc-cache -f