(Name of the other side)  Date: 
(Address of the other side)
Dear Sirs,
Re : (the Property address)
Landlord : (your name)

I/We* am/are* writing to inform you that you have breached the clause X (please insert the relevant number of the clause in the tenancy agreement) of the Tenancy Agreement signed by me/us* and you on (please fill in the date of the Tenancy Agreement) ("the Agreement"). (you can also list out the detail of the breach, for example, to sub-lease the properties to third parties, to store some dangerous goods inside the properties)

Despite repeated demands, you have failed to response to my/our* warning and let the said wrongful acts to continue. (you can deleted this sentense if it is the first time you warn the other side on the his wrongful acts)
I/We* therefore give you notice pursuant to Section 58(1) of the Conveyancing and Property Ordinance that you are required to remedy such breach of the Agreement within the next 7 days otherwise legal proceedings will be instituted against you without further notice in which event you may be liable for the legal costs occasioned thereby.
กก

Yours faithfully,

กก

กก

(signature here)

กก

(Block Letter of you name)

* Please choose one