Permalink Trouble

Hi, my blog currently uses default permalinks, so the URL structure is like this:

https://truefire.com/blog/?p=123

I want my permalink structure to look like this:

https://truefire.com/blog/sample-post/

However, when I make the changes in permalink settings in the admin dashboard, the links to the individual posts become broken. I think I have to do something with my htaccess file, but I am totally lost. Please help!

Thanks in advance ??