You can start by offering a wide variety of adult foods for the baby bird to explore (or ignore). Offer small amounts, since most will not be eaten. The goal is to encourage early exploration and experimentation. Continue to hand-feed appropriately, while the bird learns about solid foods. You don't want to reduce those feedings until your baby is comfortable eating solids.
Some examples of how to offer solids would be spreading some seeds on a plate or offering wet leaves for the baby to nibble on.
Wetting pellets or seeds and sprouted seeds might be more appealing than dry feed. Offer a variety of food, including fresh fruit and vegetables and chop, so your bird learns to recognize many types of food.
Here is an article that talks a little more about weaning:
When is the right time to wean a parrot? There really isn’t an exact answer to that question. Each species has its own timetable that can be used as a guideline, but it will vary with each individual bird of that species. The right answer to the question is: when the bird is ready. More...
birdtricksstore.com
And here is another one:
Phobic Birds by Joanie Doss
www.parrottalk.com
The main idea is to offer an abundance of options and get the bird interested in "playing" with solid foods. That will eventually lead to chewing and eating them. And the bird will naturally switch over, while you gently taper down on syringe feedings.
You want to avoid stopping too suddenly or intentionally letting the bird go hungry to force them to wean.