If your ESXi host has internet access, you can bypass the manual download by pulling the patch directly from VMware's repository using the "over-the-air" method.
If you use Dell, HP, or Cisco hardware, you should often download customized ESXi patches from their respective portals (e.g., Dell Support ) to ensure driver compatibility. vmware esxi 70 patch download link
If your hardware is too old to upgrade in-place (e.g., unsupported RAID controller), a fresh install from the updated ISO is your best bet. Write the ISO to a USB drive using Rufus or BalenaEtcher and boot from it. If your ESXi host has internet access, you
Always check the VMware Compatibility Guide before applying major updates. VMware ESXi 7.0 Update 3v Release Notes or Cisco hardware