Feeding your bird only sunflower seeds is like feeding a child only smarties to eat!!  Given the choice of smarties or fruit and veg... the child would tend to choose the sweets.   Its the same with your parrot.. and by continuing with this diet, you will definitely end up with a dead one !  Or shorten its life by years !   Introduce fresh fruit and veg.... and as perviously suggested a proper parrot mix... like Rainbow Mix...  

This alternative food have to be 'introduced' slowly... as the bird will still choose sunflower seeds.

Over a period of weeks as you decrease the seeds and increase the proper food... you should end up with the seeds being used as a treat... individually.. as a reward for tricks etc.. perhaps a doz. or so, seeds per day !!  Hand offered and not in a dish ! Your parrot will look forward to this treat... and will certainly be far more healthier.

Good luck !   Rab Macgill