Did the salon not supply you with any sort of attachment kit or advice for touching up?
A lot will depend upon what attachment method the salon used ie tape or glue.

You need to 'release' the tape or glue with a solvent and lift that area off your scalp.
You then have to clean off all residue from the base & scalp (using alcohol) in that area before re-applying tape or glue and then reattach.

Most wearers find they have to do touch ups to the front hairline more frequently than the back or sides.
You'll need a range of products, but as I say, it will depend upon what attachment your using.