This article explains the purpose of the Management interface and provides instructions on how to modify it. Here is the screenshot for the same under the Test Agent tab:

When you uncheck "Management" on eth0, you need to enable the same on another interface. Then only we can save this.

The purpose of the management interface is to establish a connection between the NCC and the Test agent. When you change the management interface from eth0 to eth1, it will use eth1 to connect to the NCC.

Refer: https://app.netrounds.com/static/3.0/support/testagents/config-gui/ta-interface-config.html#interface-tab