So you'll need to shift the data in one track along by one bar length manually. Select that track from the point where you want to insert a bar until the end of the piece. Use the Single Track Cut function to cut the content to the clipboard. Paste it in one bar later.
How to insert a bar guitar pro?
In the toolbar where all the buttons are, one should look like to bars separated with a + in between. That should be it. Just keep in mind the bar will be inserted in ALL tracks. ctrl + insert.
How to add bars in guitar pro 7?
Just as well, using the Bar > Insert Bar / Delete Bar menu will cause a bar to be added or deleted on every track. Guitar Pro automatically manages barlines.