You can't complete an SRG2156 online.
That black text in the blue box at the top which implies you should is a common header to many of their forms. What I think it means, is that on some "enabled" forms you can type your info into the data fields, then print it before submission, rather than print it then fill in by hand.
With the couple of applications that are a genuinely online process, you have to take your ID to an examiner, show them it, photocopy it, get the examiner to write the required words and sign the copy, then scan the copy and upload it with the application. Easy and simple!
