Test existing model on a different dataset

Hi,

I have two datasets which are very similar (same attributes & label), yet one of them is incomplete. The assignment is to develop a predictive model (Decision Tree and Logistic Regression) with the "incomplete" data and to validate this on the other dataset. So the goal is to develop the model with one dataset (the "incomplete" one) as training set and to use the other dataset (the "complete" one) as test set. Does anybody know if it is possible to model this issue by means of cross-validation/performance?

Thank you in advance

Viktor