Internal Server Error After changing Link Please Help!

Good Afternoon,

I’ve had this site for a while now (this is my first site by the way), When i first signed up for wordpress i made my main wordpress URL https://wordpress.wherzitattoday.com

So my admin panel was located at the url above.

i was doing some site SEO and noticed the wherzitattoday.com (my actual domain) and the wordpress.wherzitattoday.com were bring linked different

so i thought by changing the wordpress url to my main domain which it should be would fix this but it didn’t. so now my admin panel is gone, my theme is gone and my entire site is all in one page .

so i have two question

1, How can i go back to the way hit was before i changed the url
2. after i get it back is there anyway to make all link my main domain instead of the WordPress… meaning the site wherzitattoday.com instead of wordpress.wherzitattoday.com