I have purchased a van what do I post this to on quickbooks. Thanks

Hello Userenquiries3, 

Welcome to the Community page, 

So you wouldn't record this within Quickbooks itself as it doesn't need to go in the allowable or disallowable section.

You would need to record it on the actual HMRC self-assessment form sa103f and sa103s, in the capital allowance section to account for this.