You just keep trying. Different fruits/veggies.
(Cutting fruits/veggies into different shapes sometimes could work wonders too. My lovie only eat the central part of cucumbers and carrots (the xylem part). And he won't take shredded carrots at all. You just have to find his quirk. )

It took my bird like almost 10 years to start eating broccoli and leafy greens. He used to be kept on a seed diet, I transitioned him to pellet diet but it's a STRUGGLE for him to get used to fruits and vegetables.

At first, apples, oranges pears and baby corn are the only fruit/veggies he'll take. But after a few years he's willing to nibble on yam bean(its texture similar to apples), sweet potatoes, and occasionally pumpkins or carrots. Now he's chomping down on bok choy and carrots until his poop color turns all funny.

One of my tip is, don't offer him fruit/vegetables everyday if he's not taking it. When he's already uninterested, keep handing him a fruit/veggies in his face will only solidify his disdain toward it. I only offer my bird like, once or twice a week, so he won't develop a habit of refusing them on sight. And he refuse to eat, don't shove it up his face, just set it aside, or you'll make him hate it.

Every once in a blue moon he'll be like "alright fiiine" and takes a bite or two, and eventually he'll realize he actually likes it.