Please note that by default only orders less than 14 days old are displayed in the bpost tab. After 14 days, the orders will not be visible anymore!

How can I change it ?

It's possible to modify the number of day an order stays visible by modifying in the plug-in itself the constant 'DEF_ORDER_BPOST_DAYS' which is located in the following file:

bpostshm/controllers/admin/AdminOrdersBpost.php or bpostshm/bpostshm.php (following your plugin version)