Destination of tab on menu

Hi can someone help, I’d really appreciate any assistance.

On my blog at https://www.gerardknightrecruitment.com/blog/ when the user wants to navigate back to the main page of the blog/sticky post he/she will want to hit the “blog” tab in the menu. For some reason this no longer works, instead he is redirected to the post he is currently at but the url is renamed to https://www.gerardknightrecruitment.com/blog/the post name/index.php. So index.php is added to the end.

I am not sure why however, last week I was advised by my hosting providor to make a minor change to the index.php file in the main directory since I was having troubling installing wordpress here as well (I wanted WordPress here as well as on gerardknightrecruitment.com) The main directory is gerardknight.com and gerardknightrecruitment.com is a subfolder. I was told to either delete the index.php file or rename it, I renamed it and the installation worked but coicidentally or not, I now have the above problem with the direction of the blog tab at gerardknightrecruitment.com/blog.

I hope that is all clear, can anyone help?

Tim