Is there a way to take step back in ironman mode?

Yes, this is a place of questions, unfortunately, that doesn't mean you'll get the answer you were hoping for.

According to the The Stellaris Wiki, Ironman saves are designed to be irreversible. Here are some highlights relevant to your question:

• Only a single save will be stored; it is thus impossible to load an earlier save if something goes wrong (unfortunately, this includes save game corruption).
• The game saves automatically whenever almost any decision is taken (such as declaring war).
• Save files can be stored in the Steam cloud or on a local drive, but are encrypted and cannot be edited.

I'm assuming that surrendering is considered "a decision" equivalent to declaring war. It seems equivalent in scope to me, anyway. Therefore the game would have auto-saved as soon as you clicked that button.

Only a single save is stored, and overwritten each time, so there are no other "earlier saves" to go back to. As noted, even if your save was corrupted somehow (ie: by accident, not due to something you did in the game) it would still be unrecoverable.

And, the save is apparently encrypted (!) so you can't even mess with it using a third party save game editor (not that doing such a thing would be supported here on stack exchange anyway.)

I guess Paradox really takes their Ironman seriously.

Edit: I've also noticed in my own plays that an Ironman game will autosave every minute or so while you're on the galaxy map, so if you let the game run for any length of time after surrendering, it will definitely have auto-saved then, even if surrendering wasn't considered a save-worthy decision (although I would be very surprised if it weren't.)