What has Iran done to show it would not uphold Geneva conventions?

When they struck desalination plants in Bahrain would be an easy example. You can say that they are retaliatory strikes, but they are certainly against the Geneva Conventions.

Iran's use of cluster munitions to attack swaths of Israeli cities is also against the Geneva Convention (though I'd again point out that we started hitting civilian targets in Iran first).

Both sides have violated the conventions, but the US and Israel have violated them to a much greater degree (especially Israel and all their attacks on Lebanese civilians not to mention razing Gaza).