@gaetano23 I'm afraid we don't have an option to change individual letters on keyboards, however, if you wish, you may replace the entire keyboard assembly,
here's how you can do this, (see screenshot below for part numbers & click here for additional details on your device's hardware)
you may order the replacement parts on the HP Parts Store, If you've already looked for it and couldn't find it on the HP Parts Store, you may want to get it locally at the online store such as Amazon or eBay, etc...as the part numbers are universal.
P.S: Welcome to HP Community 😉
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I feel it's outrageous that HP can not provide a letter key that probably costs them 10 cents and wants me to buy an entire keyboard for $163 instead!!! Very poor customer service/business practice, especially since my computer cost over $1000 to begin with.