Incorporate into website

I’m looking to install wordpress as an addition to a preexisting website. Right now I have https://www.sample.com, and I want to set up blog.sample.com, but use the site navigation already set up. the navigation is a simple tab like structure across the top of the page.

would i have to develop a new wordpress theme incorporating this, or would the best route be to make a frame for the wordpress part and have the navigation around it?

i’m clueless right now as to the best route to take and welcome any and all feedback.

Thanks!