Hi Tron,
There are several ways to create and update device tags. The first is on the device’s page at the bottom on either creation or when updating.
Another way to add or update device tags would be in the workflow using the Device Update Node. The tag value and the tag key are both template-able so you can use data off your payload to set or update a tag key or value.
Also if you need to update your device tags outside of the Losant Platform you can always use the Device Patch API endpoint.
Hope that helps,
Erin