How am I even supposed to deal with Rumble as Fiora?

Sit under turret and do nothing.

Then tp to a well placed ward botlane after backing, get a double. And go back top with some MR and Lifesteal.

lose lane win game

look up videos on how to last hit under turret. wait for him to try to poke you under tower and see if you can get some trades back or force him to back off. cry to jungle for ganks. as for specific mechanics rumble requires good positioning to bully. force him out of that. his q doesn't work if he's running away as it's targeted in front of him so it's amazing for chasing. his e is blocked by minions and his w is just kind of boring. if you hit a vital and an e he may want to back off and shield if he gets scared. also get that doran's shield and specter's cowl for multiduplicitousness of poke resist. doran's shield is an amazing item if you're being harassed too hard to be able to hit the minion wave.