In case anyone runs into this issue like I have when trying to install things or perform other admin tasks remotely for people using TeamViewer, I wanted to share a solution that's worked for me.

If you're trying to do a task over TV, a lot of times it will only show the UAC box locally, so from your view as the remote helper it just looks like the screen is frozen and you can't enter credentials. So, if this happens, back out of whatever task you're trying to do for the moment and make it so you can remote control their computer with RDP over the open internet. Here's how:

1) Find their public-facing IP address (just open a browser and search 'what is my IP' or something)
2) You can try connecting after that, but the majority of routers have port forwarding turned off by default so it probably won't work. Open remote desktop on your end like normal, and type the public-facing IP with port 3389 appended like follows: XXX.XXX.XXX.XXX:3389
3) Make sure you're using the local pcsupport account, most times RDP will default to whatever account you're logged into on the machine you're remoting from. Just specify [remote PC IP]\pcsupport as the account
4) If this doesn't work yet (which it probably won't), proceed to work with the user to change their router settings
5) Go back to TeamViewer if still open or reestablish TV connection if not
6) Open cmd or PS and run ipconfig
7) Open browser and enter default gateway IP in address bar to access router admin console
8) Have user enter their admin password - will almost always be their wifi password. If they don't know, it's probably the random character string one set by the manufacturer and it's probably on a sticker on the bottom of the router.
9) Poke around until you find port forwarding settings, and add port 3389. Every router's firmware is different but y'all are smart enough I'm sure you'll figure it out. Mutter some tech-sounding words under your breath to break the silence if it makes you feel better.
10) You may have to reboot the router for the change to take effect. This also depends on the model of router I believe.
11) If the user is at home, their network probably is designated as private by Windows, but check to make sure. If it's public, you'll probably need to change it to private, otherwise Windows Firewall will not allow RDP connection.
12) Repeat steps 2 & 3 and you should have an RDP connection that feels just like being on campus, and importantly, will full admin permissions to do whatever you need to do. Also, unless the user factory resets their router or gets a new one, that configuration to allow RDP connections should remain persistent.
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