Hi S_Smith The self employed product is only a partial template of the actual self assessment form and accounts for allowable and disallowable expenses. As these are considered to be assets you would have to include them in the actual self assessment form you submit to hMRC in the 'Tax allowances for vehicles and equipment (capital allowances) section, boxes 49-59 if you're using the SA103F and boxes 23-26 if you're using the SA103S.
If you are using the QuickBooks Online product you can set up your own expense categories in the chart of accounts section(located in the cog in the top right of QuickBooks), you just need to pick the account type as expenses or other expenses> then pick a detail type that is the closest match and then name the expense category what you want and save and close it.
We must make you aware that we're not accountants and advise you that any information we provide you with should be qualified by a professional.
