ethics - I didn't acknowledge someone who helped with my thesis, is there anything I can or should do now?

I received help with some aspects of my PhD thesis from a tutor (proofreading and graphics). Of the help I received, some mathematical notation they provided made it into my thesis.

However, I did not acknowledge the tutor in the PhD thesis for this help (since received).

Is there anything I could (or should) do to rectify this?