This covering letter is for sending with the correct prescribed rent-increase notice. It does not replace that notice.
In England, send it with a section 13 notice using Form 4A. Give at least two months' notice, do not normally increase rent more than once a year, and check the first-52-week rule before serving.
In Wales, send it with a section 123 notice using Form RHW12 under the Renting Homes (Wales) Act 2016.
The Word template includes wording for the number of years since the last increase and a payment-method update. Edit the template before sending so it matches the notice and your tenancy details.