R6350 Trying to add a new computer to my wifi. Can't find my security key for my router

Are you talking your wifi password? 
If so, you could hardwire a pc/laptop into the router and log into it and check it. 

Or there's other tricks to finding a wifi password that you've already saved. 

https://www.pcmag.com/how-to/view-saved-wi-fi-passwords

 

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jefoust wrote:

Trying to install a new laptop and need the router security key.  Where can I find it?

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Install a new laptop on what?

 

If you have not changed the settings on your R6350, the default passwords are on the label on the bottom of the router.