PrestaShop lets customers keep her basket between his visitor sessions to finalize the order later.
This feature is handy, but uses up space in the database of your store.
To remedy this, the simplest solution would be to have the opportunity to erase the baskets directly into the backoffice of your store, but this is not proposed basic PrestaShop.
Enabling this feature is, however, the scope of everyone.
Simply open the file /your-admin/tabs/AdminCarts.php and modify line 25 by replacing $this->delete=false; by $this->delete=true; and then you can simply remove the baskets individually by clicking on the red line at the end of each basket, or by selecting them and deleting them en masse to go faster.
It should in no way erase the racks corresponding to commands as this will cause errors on certain functions like editing of pdf invoices.