There is often a 'half click' or 'trim' on the left shifter - if the chain is on the extreme ends of the cogs on the back, you can push the shift levers lightly and the derailleur will move a tiny bit to get rid of the rubbing. If the rubbing is happening when on the larger cogs (easier gears) at the rear, then you would tap the smaller shift lever. If the rubbing is on the smaller cogs (harder gears) then you will probably trim it with the larger lever (the one you also use to brake).
There are loads of online instructions if you want to readjust it, but front derailleurs can be a bit of a PITA.