You do not need a new license to install it on a second computer, but you cannot use both installations at the same time. From the support FAQ [https://www.simplify3d.com/support/faq/
Installation: The software can be installed on up to 2 computers that you personally own and use.
Usage: You can use the software on 1 computer at a time.
For example, if you had a laptop and a desktop, you could install the software in both locations, but you should only use the software in 1 location at a time.
Please note: Simplify3D licenses are sold as individual user licenses. A single user license should never be shared by multiple individuals.