Concatenate 2-3 table field values in 1 table field in access
You shouldn't need to concatenate the fields at all. You can find out whether a customer has filled out the survey for a given month and year by using all 3 columns: 

SELECT * FROM Surveys 
WHERE CustomerID = 1 
AND SurveyMonth = Month(Date())
AND SurveyYear = Year(Date())


The Date() function returns the current system date. The Month() and Year() functions return the month and year, respectively, of the date passed to them.

A suggestion: store the entire date a survey was taken as a Date type in the database rather than using separate columns for month and year. This will simplify lookups and storage, making the query above look more like:

SELECT * FROM Surveys 
WHERE CustomerID = 1 
AND Month(SurveyDate) = Month(Date())
AND Year(SurveyDate) = Year(Date())


where SurveyDate is a column of Date type.