https://download.eset.com/com/eset/apps/home/essp/latest/essp_nt64.exe
Explanation of the link:
Some advanced users confuse the product installer with offline virus signature updates. ESET offers separate ZIP files containing the latest signature database (usually 33-50 MB) for computers that cannot connect to the internet at all. These are not the product installer.
If you have a fully air-gapped PC, you need both: First the offline installer (via USB), then regularly download the offline update file from ESET’s website and apply it manually.