What is the best phrasing to use to say thank you in this situation?

There was this errand I needed help on for sometime in the upcoming week. I asked someone for help verbally and the person said that he could help. I am now writing to provide logistical info (time/location/etc.) to the person.

What is the best way to say thank you here? (Person hasn’t actually done anything yet, but seems willing to do so)