macOS High Sierra dmg download for making bootable usb insttaller

My old Macbook Air needs a clean reinstall as the disk was erased and no os on it. Currently, macOS High Sierra is the best option but I am unable to download the dmg file from Apple website. It only holds download for high sierra install app which only works on old Intel Mac. Is there any app to let me download high sierra dmg file and create a bootable usb installer from it?