How to make entities harvest stuff?

Hi, I wanna ask if there is any possible way how to make entities harvest some kind of a bush-type plant

Here is the code we have come up with so far

Basically what this code is supposed to do is that the entity scans an area in a 3x3x3 radius if there is the grown plant block and then its supposed to replace it with ungrown plant block + drop the items.

Atm it only makes the creature walk close to the block but then nothing happens and we dont know how to fix it.