VAT for NATO Visiting Focres to the UK

I am a member of NATO Visiting Forces, posted in the UK. A relief of VAT for consumer durable goods may be available to me, under certain conditions (VFR03200). I understand that a refund of the VAT may be obtained from HMRC. However, it is not clear to me how it is done or how I can contact HMRC in this matter. Any guidence would be apprechiated. /Mikael