To add, update or remove a NTP (Network Time Protocol) setup, you need to go to IoT Server Configuration application and select the NTP Server entry in the left side menu.
When you currently have no NTP Server setup you will see the following main page with a large Create a new NTP server button in the middle of it. By clicking on this button or the equivalent one on bottom - right, you will access the ability to setup an NTP Server.

A drawer displays on the right side of the screen, first set the URL or IP address of the NTP Server to the Target (1) field then click on Create (2) button to apply your setting. This is confirmed by a green message displayed on top right.

In case you later need to edit the NTP Server configuration previously created, you can Edit (1) the entry by clicking on the corresponding pencil icon:

Then you can modify the NTP Server configuration entry editing the DNS or IP and save your modifications by clicking on the Edit button. A configuration messages will be displayed top right.

When you need to remove an existing NTP Server configuration, simply click on the Remove (1) icon, represented by a trash icon.

A popup will be displayed asking for your confirmation:

Confirm your choice to delete the NTP Server Configuration, a green message displayed top-right will confirm the deletion and the NTP Server entry will be removed from the list.