Mass update all cells in a column with a substring of it’s original value

I need to trim the last seven characters off of all the cells in a column.

This query returns the results that I need

SELECT test_date, SUBSTRING(test_date FROM 1 FOR CHAR_LENGTH(test_date) - 7) as test from results; 

I now need to take the computed result from the substring and replace the original values.

Here’s what the data looks like, if it helps.

Data Table