You can submit tabs via the Submit Tab button. On desktops the button is always in the left toolbar. The tab should be in *.gp5 format. To create a tab you'll need:
Windows/Mac: buy Guitar Pro software or use a free TuxGuitar alternative.
Android: use a free TuxGuitar app
iOS: you can create a new tab in the Guitar Pro app but it doesn't support export to *.gp5 format.