How to use date variables in prediction.
You can preprocess the date variable while making predictions in similar manner that you have done during the training time.
If you could give more information on what type of problem you are trying to solve and about the target variable, that would help us in giving you better suggestions.
In general, you can have a date variable with either regression/classification problem or a time series problem. In the first case, you need to extract features from the date column (such as day, month, year, day_of_week, weekend_or_weekday, etc) and drop the date column. Regarding a time series problem, you can use the date variable (convert it into datetime format) and use it as input for arima or prophet (there are many other time series forecasting techniques)