After you upgrade to ESXi 7.0, you must apply a vSphere 7 license.
If you upgrade an ESXi host to a version that starts with the same number, you do not need to replace the existing license with a new one. For example, if you upgrade a host from ESXi 6.5 to 6.7, you can use the same license for the host.
If you upgrade an ESXi host to a version that starts with a different number, you must apply a new license. For example, if you upgrade an ESXi host from 6.x to 7.0, you need to license the host with a vSphere 7 license.
When you upgrade ESXi 6.5 or ESXi 6.7 hosts to ESXi 7.0 hosts, the hosts are in a 60-day evaluation mode period until you apply the correct vSphere 7 licenses. See About ESXi Evaluation and Licensed Modes.
You can acquire vSphere 7 licenses from My VMware. After you have vSphere 7 licenses, you must assign them to all upgraded ESXi 7.0 hosts by using the license management functionality in the vSphere Client. See the vCenter Server and Host Management documentation for details. If you use the scripted method to upgrade to ESXi 7.0, you can provide the license key in the kickstart (ks) file.