When you say statement of service, are you referring to employment reference letter? If so, there's no particular template but you just have to include all the details the assessing authority wants in there i.e. Company name, country, job title, number of hours work per week, job description, etc. Usually you'll find this info in the assessing authority's checklist. Sometimes also you can find a template sample on their website. It just really depends which assessing authority you're dealing with. You need to be careful on this part as they are usually nitty gritty on this and a tiny oversight may lead to an issue, worst would be negative outcome. A lot of my clients get stuck with this wherein we spy minor errors which they didn't realise and have to do it again - time is wasted in the end. It may look simple because it actually is but most often than not, applicants still miss out on few tiny details due to human error. Out of curiosity, what's your occupation?