Generate Menu Access Keys
Jelly, 41 bytes
e/€S;eḲ1ịⱮƊ}¥/€;=Ḣ¥/€µS
LØAœ!ż€³Œu¤ÇÐṀẎḢ€

Try it online!
This is really messy and also O(26^n) lol.
Explanation: literally just brute forces it ._.
-6 bytes thanks to caird coinheringaahing