Adjusting Prior Year Tax Computations - UK Limited Company

On review of my accounts from past years I can see there was a mistake made within the tax computations, although the micro accounts submitted were correct. Losses were made in those years. However the losses, in reality, were greater than the amounts in the tax computation. The accounts were prepared and submitted via the HMRC portal. The micro entity accounts are correct but the tax computation is not. The periods are: 01/12/17 to 31/11/18 and 01/12/18 to 30/11/19 for £1,506.65 and £1,524.05 respectively. Please advise if these necessary changes can now be made. And if so how to do this. Kind Regards

Hi Andrew Doyle,
Once the time limit to amend a company tax return has expired, the company loses the right of amendment. 
It is too late for the tax assessments for the accounting periods ended 30/11/2018 and 30/11/2019 to be amended to change the figures of trading losses. 
The company may be able to use the additional trading losses against profits of earlier periods by making a claim to overpayment relief.
Please see:
SACM12057 - What the person can claim: Losses
If overpayment relief is not claimed, prior-year adjustments are usually reflected in the latest tax return.
HMRC guidance can be found here:
BIM34020 - Change of basis of computing taxable profits: what are invalid and valid basis?