Amending Self Assessment submitted through 3rd Party Software

HI, I need to submit a correction to my Self Assessment that was submitted online by my former accountant. The accountant used 3rd party software to submit and I am unable to amend this online as a result through my own login. I no longer use that accountant so I was wondering if I can submit a revised Self Assessment by paper? TIA

Hi ,
 

Write to us specifying which boxes you would like to amend, and we can update your return for you - you can find the address to write to here : Self Assessment: general enquiries  . We may also be able to update your return if you contact us by phone or webchat . Thank you .