Need Blog assistance

We installed a new plug-in called ‘permlinks master’ for the navigation bar to link all the pages to our homepage. We activated the plug-in by going to ‘Settings’ and perm-links and when we tried to change the URL to the blog site and put it back afterwards, saved it, and then it read:

“Error 404: NOT FOUND! Your browser cannot find the document corresponding to
the URL you typed in.”

Can you help us with this?

Best,
Tina