This is not a node you can directly invoke with the SHIFT + A submenu. Here is how to do it :
- Create your loop and click it to select it
- Assign a parameter
- Go to the right-side panel (shortcut N, or click on the arrow on the right side of the animation nodes node tree)
- Go to the "Node" subpanel
- Click on the "Reassign" button next to the parameter socket
- Click in the node tree window where you want to place the "reassign" node
If you want to have the "Condition" boolean operator in the node, you should :
- Select the "Reassign" node
- Go to the "Item" subpanel on the right
- Turn on the computer screen icon next to the "Condition" input socket.
This works for all the animation nodes which may have hidden input/output sockets
