Hi @IlariaHenein,
I'm fairly sure all LTI tools added to global navigation in the official way would be just above the help icon. In this case, Canvas determines the order of the icons (I think it's done in the order in which they were installed, but I could be incorrect).
If you have an icon below help, that leads me to think the icon itself is being inserted by custom JavaScript/CSS in your Canvas theme instead of an LTI placement. It sounds like you're familiar with JavaScript/CSS in the theme area, so I'd suggest checking the files you have in place now to see if the icon is being inserted through there. Once you're able to determine that, someone might be able to give options to adjust the placement.
I hope this additional info may be of some help.
-Chris