Migrate old blog to new one

I hope this makes sense. I let a domain go which had my blog on it. All the files are still on my server. I have another domain which is on the same server that has my new blog set up on it. I want to transfer the old blog to the new one. What do I need to do? Which files do I need to transfer? It doesn’t matter if anything gets overwritten on the new one.

Also, the theme and other customizations don’t matter. I just want the posts transferred.

Thanks,

Bernie