Copy the file(s) you'd like to override from `./node_modules/@hyas/doks-core/` and paste to `./themes/my-doks-theme/`. Make sure to keep the folder structure.
If needed, you can change the mountings settings in `./config/_default/module.toml`. See also the Hugo docs: [Module Config: mounts](https://gohugo.io/hugo-modules/configuration/#module-config-mounts).