The first thing you need to do is read the BenefitsandWork guide on completing the UC50. You will find it in the Guides section " Employment & Support Allowance and Universal Credit Claims On Physical & Mental Health Grounds " www.benefitsandwork.co.uk/?dlp=673eda9b178bf The section on completing the UC50 is from page 29 onwards.
The second thing I would advise is gathering your supporting evidence. You can find advice on doing this from page 111 of the guide.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems