I believe the number of a given date correspond to the number of days since 1/1/1900. So you could in python count the number of days between those two dates using datetime.date object.
For example : date(2020, 7, 11) - date(2020, 7, 2) = 9
Then you replace the date value by the number you just calculated.
That said I believe it is still better to fix the problem at the source rather than in python as suggested in the comments
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