several things you can try. put a piece of paper/cardboard under the A string at the nut[the nut slot may be too deep]
raise the action at the saddle[a sliver of an old credit card placed under the saddle]
put a straight edge down the neck and see if the fifth fret is high, tap it down [or file/sand it] if it is. The first 2 are temporary possible fixes to see if that's the issue. a new nut or filling the slot and recutting, and /or a new saddle are the right way. you can buy professional tools, or improvise. I use a mini hacksaw blade with the sides ground down [thinner cut] and/or welding tip cleaners for the nut. For fret leveling, I mark the frets with a black sharpie and use my super flat diamond wetstone to see if the frets are level. Use this at your own risk, I am not a pro.
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