Hi,
You cannot fill in part of the tax return online and the rest on paper. The whole tax return must be filed together in the same format. If you are reluctant to buy commercial software to submit the tax return online, your only option is to submit a paper tax return. You can find the tax return and supplementary pages here:
Self Assessment tax return forms
The address to send the tax return to is on the front page of the tax return.
As the deadline for paper tax returns was 31 October, there will be late filing penalties applied. You can appeal those penalties, using the appeal form here:
SA370 Appeal – Self Assessment: Appeal against penalties for late filing and late payment
Thank you.