is there something to fit over guitar strings to play chords easily?

Answer 1

Your fingers?

Answer 2

There's something called a 'capo' that presses all the strings down at a certain fret so you can play in a different key without using bar chords. That would make it easier if you don't have the strength in your hand to play bar chords.

Answer 3

Are you thinking of a capo? A lot of guitar players used them.