To obtain a landlord approval letter, you must first ask your landlord for permission to sublease your office space. This can be done by sending them a formal request letter, either by mail or email. It should include your name, address, and contact details, the reason for wanting to sublease the space, the name, address, and contact details of the potential subtenant, and the proposed sublease terms such as start and end date, rent amount, and security deposit. Additionally, you should include a copy of the sublease agreement that you and the subtenant have agreed on, a statement that you will comply with all terms and conditions of your original lease agreement, and a request for a written approval letter from your landlord. Supporting documents that demonstrate the credibility and suitability of the subtenant should also be attached, such as a credit report, reference letter, or business plan.