Migrating from Non WordPress site to WordPress site

I’ve got myself a but confused and need some help. I’ve got a site e.g. example.test.com and I have created a new WordPress site on dev.example.test.com. What I need to do is not only maintain the SEO for example.test.com but also re-direct the urls to dev.example.test.com AND the url ‘appear’ like it is example.test.com. I’ve got the re-direct working (using .htaccess) but do not know how to make dev.example.test.com appear as example.test.com? Any suggestions? or am I trying to do something unachievable?