I have never tried it, however, in config.php there is a section for date formats:
'date_formats' =>
array (
'Y-m-d' => '2010-12-23',
'm-d-Y' => '12-23-2010',
'd-m-Y' => '23-12-2010',
'Y/m/d' => '2010/12/23',
'm/d/Y' => '12/23/2010',
'd/m/Y' => '23/12/2010',
'Y.m.d' => '2010.12.23',
'd.m.Y' => '23.12.2010',
'm.d.Y' => '12.23.2010',
),
'datef' => 'm/d/Y',
I assume that, if you edit this section yuo should be able to achieve what you are looking for.
For example, you could modify it to:
'date_formats' =>
array (
'Y-m-d' => '2010-12-23',
'm-d-Y' => '12-23-2010',
'd-m-Y' => '23-12-2010',
'Y/m/d' => '2010/12/23',
'm/d/Y' => '12/23/2010',
'd/m/Y' => '23/12/2010',
'Y.m.d' => '2010.12.23',
'd.m.Y' => '23.12.2010',
'm.d.Y' => '12.23.2010',
'd/m/y' => '23/12/10',
),
'datef' => 'd/m/y',
Instead of doing this in config.php, which is vulnerable to rebuilds of the file, you may do it in config_override.php.
However in this file you have to enter it in a different way:
$sugar_config['date_formats']['d/m/y'] = '23/12/10';
$sugar_config['datef'] = 'd/m/y';
Another solution would be to correct it in the database. I am not giving you the sql statement because I am not sure of the effects it may have. This has to be done with extreme care not to change irreversibly values that shouldn’t be changed.
My last comment is that, if you want a really functioning system, the year has to be the full year (yyyy, eg 2018) and not just made with ywo digits (yy eg 18) only. This is because your searches, reports, sorting, etc, will fail if your data is inconsistent.
Just imagine sorting 17, 18, 2017, 2018 or searching for something after 01/01/2018: you will not get those with year 18!!!