You have to do some basic string manipulation. The steps are:
1. Search for "Dear customer", using the at() command. This will give you the position where "Dear customer" starts (or zero if not found - you should do some error-checking).
2. Extract everything after that position; substr() seems appropriate here.
local lcSearchText
lcSearchText = "My customer"
replace MyMemoField with substr(MyMemoField, max(at(lcSearchText, MyMemoField), 1))
Not tested exhaustively. The max() ensures that you start, at least, at position 1: Otherwise, if the search text is not found, you would start at position zero; and a quick test reveals that would return an empty string (and therefore eliminate your entire memo field).
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)
