You can use this script to do the conversion:
You will need to checkout the repo and install the requirements first:
git checkout email@example.com:edx/configuration.git
pip install -r requirements.txt
You will likely want to pass in your auth.json in addition to your env.json, as the LMS now only reads from a single yaml file. You will want to repeat this process for the lms and studio.
Simply feed your json in like so(it can handle multiple ones):
python merge_json_to_yaml --files lms.env.json --files lms.auth.json > lms.yml
python merge_json_to_yaml --files cms.env.json --files cms.auth.json > studio.yml