Run a query such as this to generate the update statements, copy those update statements to an SSMS query window and run it.
SELECT 'Update ' + LEFT(field1,CHARINDEX('.',field1)-1) + ' set ' + STUFF(field1,1,CHARINDEX('.',field1),'')
+ ' = YourNewValueHere'
FROM FieldList;Please do review the generated SQL statements to make sure that it is correct and that that is what you want to do.
You could also make those statements into a dynamic SQL string and then use EXEC or sp_executesql to execute that dynamic string.