Accountants
If you are a limited company, you will need to employ an accountant.
If you are a sole trader / self employed but the thought of having to deal with anything financial brings you out in hives, then you need to collaborate with someone who has those skills, or employ an accountant.
Bookkeeping
If you are scared of doing your own bookkeeping, because you've never done it before, but really feel you want to have these skills , then hire an accountant to talk you through what information you need, and how to collate it. HMRC also offers good free introductory courses on bookkeeping for the self employed, or again collaborate with someone who has those skills. You can then do your own bookkeeping throughout the year and get an account to submit your tax return or....
DIY Tax return
If you are interested in your finances, and can work your way round a spreadsheet, then HMRC have made it much easier in the last few years to file your tax return on line without an accountant. Use an online programme like Quickbooks , Sage or Xero or a free programme like Wave, to get your incomings and outgoings calculated, and then do your tax return yourself online.