Are you saying that you need to migrate the whole site? If so, you will ideally need all the files on the WordPress install and an export of the database. This is the simplest way.

Let me know if you need any help.

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The reason to try this first is that if (when…) it doesn’t work you can go back to the people that gave you that file and show them that it hasn’t worked and ask for a better alternative. As spidrweb said, the best way to do it is a full backup of all of the websites files plus a dump of the database.

If they can’t do that there’s a few other options like some backup plugins, so you could explore those too.

After that if you can’t get any assistance from the current people, get back to your client and tell them that you can’t move forward until you get their assistance.