if your phone doesn't have a restart feature (which would be quite rediculous, haven't seen an Android phone like that), and you can't figure out how to use something like Xposed, then the Play Store is your only real option.
My Motorola Droid Razr Maxx didn't have a reboot option in the menu (although Power + Vol Up for several seconds would reboot). I don't think a reboot widget would work without root. My solution was using a widget from Rom Toolbox Pro, which I placed on the far corner of the left-most homepage, which had nothing else on it, so I wouldn't accidentally tap it. It required Superuser permissions, so I'm pretty sure such a thing would only work if the phone is rooted.
I'm guessing this Karbonn phone has a removable battery, because any phone with a non-removable battery should have some emergency reboot method.