Have a look at the AIP and contact them using the provided information within:
EGLC - London City
A nominated handling agent is mandatory for all visiting aircraft. Handling for corporate and General Aviation by arrangement with London City Airport Jet Centre, Tel: 020-7646 0400; Fax: 020-7646 0450; SITA: LCYGAXH
Alternatively, use their website and read up on the details:
London City Airport
Handling Agents
Air France (inc baggage enquiries) 0870 850 1839
Corporate Aviation +44 (0)20 7646 0400
Execair Cargo Handling +44 (0)20 7646 0660
Alitalia Baggage Handling 0870 225 5077
KLM Baggage Handling 0871 222 0522
Aria Baggage Handling for Lufthansa +44(0)871 945 9124
Aria Baggage Handling for Swiss +44 (0)20 3203 0325
Aria Baggage Handling for BA +44 (0)20 7646 0782