Declaration of Honour sounds right to me.
but ...
My guess is there's a section of the document where the declaration is made (i.e., where the applicant provides their particulars and then signs) - and the declaration might typically read "I declare on my honour ..." so this section of the document could be where the "Declaration on Honour" , if you like, is made - and maybe it can refer to the document itself?
In which case, both Declaration of Honour and Declaration on Honour might apply?