How do I insert text above a table at the top of a Word document?

The active cursor is even with the bottom left of the table normally. You can just hit Ctrl+Home to get to the very first character of the file, then Enter to move the table down.

If your table is positioned after the section break, or on top of any other page, or anywhere else for that matter, place the cursor in the top left cell of the table, and hit Ctrl+Shift+Enter to insert a new line before the table.

If you've built a table that encompasses many pages and forgot to add a title on top of subsequent pages, which has happened to me quite a few times, I find that inserting a section break at the top left corner of your table (inside the first cell) gives you the space you need to copy and pace the title. Then you simply delete the section break (or not) and go about your life.

Insert a new row to be a blank first row. Convert table to text. Done.

You need to ensure that your table vertical position is "Bottom" relative to margin otherwise new row keeps appearing on the previous page.