YOAST SEO PLUGIN PROBLEM

Thank you all for reading my comment.
I am new to WordPress and basically I work for a company where part of my job is to update web content on a WordPress Site.

The company that was given the contract to design the website wants to rip me off because they wanted us to pay for SEO and I told my company that I can handle it after I’ve through Andrew Williams tutorials on wordpress.

On January 2nd, I installed Yoast Plugin and edited the settings for XML Site Map because it sitemap wasn’t working.

Below code is the current .htaccess file of WordPress SEO by Yoast Plugin file Editor. I got the code that stated from line # BEGIN WordPress from a website that advice I edit the file editor if my site map is not working.

# BEGIN iThemes Security – Do not modify or remove this line
# iThemes Security Config Details: 2
# Enable the hide backend feature – Security > Settings > Hide Login Area > Hide Backend
RewriteRule ^(/)?backgateaccess/?$ /wp-login.php [QSA,L]
# END iThemes Security – Do not modify or remove this line

# BEGIN WordPress

RewriteEngine On
RewriteBase /
RewriteRule ^sitemap_index.xml$ /index.php?sitemap=1 [L]
RewriteRule ^locations.kml$ /index.php?sitemap=wpseo_local_kml [L]
RewriteRule ^geo_sitemap.xml$ /index.php?sitemap=geo [L]
RewriteRule ^([^/]+?)-sitemap([0-9]+)?.xml$ /index.php?sitemap=$1&sitemap_n=$2 [L]
RewriteRule ^([a-z]+)?-?sitemap.xsl$ /index.php?xsl=$1 [L]

# END WordPress

The reason I edited this was to save our company from paying so much on SEO.

I have uninstalled Yoast Plugin but my problem still there. The website is heightsaccess.ng and when you open it, the website opens the home page but other pages doesn’t open anymore.

I will appreciate it if someone can help me resolve this issue since our site has been down now for a long period.

Thank you once again for your consideration.