Which tool should I use?

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Hi everyone! I'm writing thesis on Customer Satisfaction in restaurants, and will distribute questionnaire to the restaurants. I will modify the SERVQUAL instrument a little bit, so what model should I use to ensure the modified instrument reliable? Also what tools should I use to ensure the reliability and validity of the questionnaire? Should I present the Reliability and Validity analysis before distributing the questionnaire or after? Thanks a lot!:)