the problem is that you are modifying the code by hand rathwer using the data assist search behavior to create the code.
first, on the results page, open the bindings panel and select Form Data, click the folder icon and select the search page to add bindings for the search page form elements.
now double click the data assist search server behavior.
click the plus button to create a new criteria, select the columns that will be searched and other criteria options.
for value, click the lightning bolt icon and select one of the search form bindings.
repeat this process for the other two search fields.