I have the problem that I use the citation manager Citavi and it can only export in the format urldate = {dd.mm.yyyy}. However Bibtex needs the format urldate = {yyyy-mm-dd}. It is not really realistic in my case to change all the dates of my bibliography manually, as I have many entries and after each export I would need to redo it.
For example my bibtex entry looks like this:
@Misc{FAO.2011,
Title = {{FAOSTAT: Food balance sheet}},
Author = {FAO},
Year = {2011},
Address = {Rome},
Url = {http://faostat3.fao.org/download/FB/FBS/E},
Urldate = {15.1.2014}
}
Then I receive following warning, when I compile it with BibTex
Package biblatex Warning: Biber reported the following issues
(biblatex) with 'FAO.2011':
(biblatex) - Datamodel: Entry 'FAO.2011' (literature.bib): Inval
id format '15.1.2014' of date field 'urldate' - ignoring.
Is there any way to change the format of Bibtex that it reads the urldate in format urldate = {dd.mm.yyyy} or can I convert it somehow to urldate = {yyyy-mm-dd}?
I have searched in the internet and haven't found any solution for this problem. It seems to be a specific problem of Citavi. To bad that Citavi is not customizable.
My question is similar to this: Ignore a bibliography field [e.g. "urldate"] for eliminating of biblatex/biber warnings. However, no solution was provided in this topic for my problem, because in this case urldate was not needed and thus just ignored. But I need to give urldate.

\documentclass{...}and ending with\end{document}. – Feb 19 '15 at 18:07