dear Rizal,
Steps to converge are .
1. first check that d.o.f is zero
2. then go to your crude assay and check how much naphat %, kero % and diesel % reamining is Atmos bottom,
input all theses values .
check the duties and TPA , MPA flow rates and return temps. accordinging to the tray temps.
3. if you have modles whole atmospheric column section as whole , then you need to first converge colum only then whole flow sheet.
I hope your case converges,