what documents are needed with form SRG 1104?
This is an 8 page form and all the requirements are clearly listed in Guidance Note 3 on the 8th page marked i of i
GUIDANCE NOTE 1 (above) tells you who can certify documents, if you do not follow that requirement you will either have to send them the original or take it in yourself. I suggest the latter or you will not be able to legally fly until you get it back.
You need the HT of any FTO/ATO, look one up and go see them, there is one on most airfields.