You need to report the loss of any keys to your landlord/manager. If the landlord/manager has a spare key, you might be able to use this in case of missing keys or locking yourself out. If the landlord/manager cannot be reached (e.g. outside office hours), you’ll need to call in a professional, certified locksmith to replace the locks. You can find one on the CCV website, for instance.
The landlord/manager must receive a copy of the keys for the new locks as soon as possible. It may be necessary to replace all the locks anyway following the loss of (one of the) keys on security grounds.