Start writing down the bash commands that you use to build and deploy your app locally.

For manual steps just write down a description to make a "do-nothing script" [1] to transition with gradual automation .

Then you can turn those into the rough draft of your CI/CD a pipeline.

If you use a common system there might already be adapters for your CI/CD platform of choice to make it even easier.

GitHub Actions is a good simple system to start with if your code is on GitHub.

[1]: https://blog.danslimmon.com/2019/07/15/do-nothing-scripting-...