Available with 3D Analyst license.
To add individual nodes to an editable TIN, use the Add TIN Point interactive tool 
from the TIN Editing toolbar.
When the tool is clicked, a dialog box appears that enables you to specify the height properties for the digitized points. The following steps describe how to interactively add points to a TIN surface.
- Click the TIN Editing drop-down arrow and click Start Editing TIN.
- Click the Add TIN Point tool from the TIN Editing toolbar. The Add TIN Point dialog window appears.
- From the Add TIN Point dialog window, set Height source to either From Surface or As Specified. When the From Surface option is selected, the elevation of the digitized TIN node is interpolated from the selected location on the surface. When the As Specified option is selected, the digitized TIN node is specified in the height field.
- Enter the new elevation points onto the TIN surface by clicking the desired locations.