Replace values with text contains

I Have this table

and I have to replace some null values with "school1". The problems is:

- the problem is always with school1;

- I need do take the email domain as a key to identifying the missing values from school1; 

- If I have other null values in collumn SCHOOL different of "school1" must continue null, but all lines that have @school1 in USER must have school1 in SCHOOL.

I tried this formula, but it fail

= Table.ReplaceValue(#"Filtered Rows", each [SCHOOL], each if Text.Contains([USER], "school1") then "school1" else [SCHOOL], Replacer.ReplaceText, {"SCHOOL"})

It didn't change at all the table. What am I doing wrong?