The error message about undefined
\aclabelfont is independent from package
scrlayer-scrpage. I do not known, which package needs it but redefines it instead of defining it (
acronym, e.g., would need but also define it). Maybe you are using a not well defined template.
Nevertheless, as you can see from the CTAN Catalogue entry of
scrlayer-scrpage the package is part of the KOMA-Script bundle. You should not try to download and install
scrlayer-scrpage.sty without a complete KOMA-Script installation, because the package depends on other parts of KOMA-Script, e.g., package
The link above also documents that MiKTeX and TeX Live knows KOMA-Script as package
koma-script. So you can and should simply use the package manager of your TeX distribution to install it. Experienced users can also use KOMA's package repositories to install a current pre-release of KOMA-Script or to download a TDS-archive. The TDS-archive of the current official release is also available from CTAN.