Please help us help you and fill where relevant:
Your LimeSurvey version: 6.15.19+251017 
Own server or LimeSurvey hosting: University of Coimbra
Survey theme/template: herdar [fruity]
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I imported one survey into another, assuming that the two would be combined. However, the imported survey replaced the existing one and I lost the survey I wanted to expand. Is it possible to recover the previous version of the survey? 
Thank you very much for your help.

Did you ever save the first survey (possibly for sending it to another person)?

Else I would not know a solution.

Tammo