Though I feel like we can go even further in confirming with the customer (in an ideal world of customer satisfaction).
Go back to the customer(s) to tell them what you’re doing about it, and after the fact go back and tell them what you’ve done, rather than just poll them again via NPS.
Sure, they may notice an improvement, but they also may not relate it back that it’s in response to the feedback they gave. Makes them feel as if their input is read and valued. It also helps confirm that you’ve addressed their issue to their satisfaction.

Again, in an ideal world. May be tough to do depending on the scale of the environment, though a well worded group email to those that gave feedback related to that ‘bar’.

Thoughts?