R6400 "Failed to obtain IP address"

I had a two-day internet outage from provider, but initially tried to troubleshoot lack of internet on my own. I believe I clicked on my router's connectivity choice of manually optaining IP address (not recommended) and now that my internet has been restored, I'm having trouble connecting via wifi to any wifi devices that I had previously had using my router.  Ex: my smartphone cannot connect to wifi from my router, says "Failed to obtain IP address".  My smart TV also has this problem.  I have tried to manually put in the IP address that router says I have.....on my computer's networking settings (changing from dynamically finding address)....but won't save the number I put in.  I really need help.  Is it possible to go back to factory settings on my router, and how would I do that? Would it fix my problem?  Thank you for your suggestions.