Even though I don't agree with this way of thinking I can give you a few ways.
If you want to eradicate homosexuality or at the very least minimize it you need to identify the allele responsible for increasing chances of being homosexual and edit it to display the normal variation.
But all this will probably still not get rid of it because environmental factors still have a large say in who people find attractive.
Genes only really sorta influence our behaviors
Yeah, I would not bother with the gene excuse. There is a slow but steady movement away from explaining complex traits with specific alleles. The coming paradigm is that virtually all genes affect one another: the "omnigenic model". Genome wide-association studies (proper science) is what has enabled this as opposed to garbage, unreproducible social science studies.
Ultimately, the need to justify homosexuality with science is inherently pathetic as science is, nowadays a mode of instrumental reason. As a result, it does not have any values or ethics of its own and does not discover any. Instead, it merely adopts the values and ethics of the society from which the scientists come from.
Ergo, it is not science which justifies homosexuality but rather the overarching liberal society in which that science is conducted. Be brave and justify homosexuality on the basis of liberal thought as opposed to just saying, "bUt ScIeNcE!".