Once Ive printed my completed form, can I then add a few more details onto it?

I thought I completed my application form in online correct. Then once I'd printed it and read through it in front of me I realised that I needed to add a few more details onto it. Can I just write them onto the form or do I need to redo it online then print off the updated version. I know I cant get back into my original one as I have submitted it to print.
Thank you for your help