Perhaps nucleofilic attack of the nitrogen of the amine, substituting the cyano moiety

Ethylenediamine proceeds quite readily at the reflux temperature of dry benzene to yield cyclic N-cyanoguanidine by removal of two ammonia molecules, and thus, formation of two bonds of the type C-NH-C.

For more information, see the reference below:

"Synthesis of cyclic N-cyanoguanidines"

C. M. Baltzer , C. G. McCarty

J. Org. Chem., 1973, 38 (1), pp 155–156

first u prepare HCl salt with ethylene diamine in water at 5.5 to 6.5 pH then add cyno guanidine then heat it to 50-55°C for 2-3 Hrs then you can get your desired product