The answer is: insert the gene responsible for larger sized kernels into the genome of the corn with smaller sized kernels and a high yield.
The techniques of genetic engineering are used to introduce hybrid genes for some desired substance or trait into the genome of other organisms. Here, the desired trait is larger sized kernels. So, the gene responsible for this trait will be inserted into the genome of the corn with smaller sized kernels and a high yield.
It should be taken into consideration why two other choices are not correct:
1. there are no genes for less or more of something in the genome.
2. genes are part of a genome, so the genome for a trait cannot be inserted into a gene of an organism.