You may want to ‘try’ if they’ll accept pellets. All of my birds over the years have taken right to them in a dish. That’s not what I hear from everyone, so perhaps I’ve been lucky with every single bird. You might want to take all other foods out temporarily, and place the dish in a usual food spot, and see if there is any interest. If they even go and examine it curiously for a few moments, it’s a pretty good sign.
If you have a variety of different foods at the same time in the cage, it typically takes a long time for them to try a new food.
As Sim mentioned; we do not condone mirrors in the cage. It might work, but I would suggest this as last resort, and once the budgie is eating and accepting the food, to remove it.