to be clear, i've not had this problem! but i have toyed around in blender for my models (primarily to make xwear stuff)

> looking online it seems to be a common problem and the only solution i found was to check the eye bones, but i cant seem to find them in unity and .vrm files dont open in blender=

two (threeFOUR even) different answers to this:
1. https://github.com/absolute-quantum/cats-blender-plugin is what a lot of people use when working on vroid plugins (esp ones with video tutorials!!), but it only works on an older version of blender. You're going to be able to find the most tutorials for this!
2. https://cats.neoneko.xyz/ provides a version that's more up to date! but it lacks a "Fix model" button and i've not found a youtube tutorial using it.
3. https://toolkit.neoneko.xyz/ the new cats team (the reason there is an updated version from a different team is that old maintainer disappeared) seems to have developed a new tool, i have literally learned about it as of writing this post and I know nothing about it.
4. https://vrm-addon-for-blender.info/en/ is the most basic one and what i'd use if i were making a .vrm model entirely from scratch. *AS FAR AS I KNOW* you need this installed regardless. It'll do imports & exports and might be enough to just flip the eye models around.