if the date column really contains date values, you only have to change the format.
So format the cells with Ctrl + 1 and then select the correct format for number categories.
If your date column contains strings, the easiest way to convert them into a date format is to use [Data] [Text in columns]. Then select your preferred format. Done.
If you want to use Search and Replace to replace the commas with dots in any case, you only have to select the column you want to replace before you execute the command. Then only there will be replaced.
I hope this helped you.
If this answers your question, please click on the white hook in the grey field. Only the author of the question can do this.
If you have any questions, please comment this answer or your question.