Deployment advice

I started my career in an MNC, worked there for 1 year as an SQL developer. There we used DBeaver for deploying files. Since I was a fresher/trainee, lot of the deployment work was handled by my seniors.

Now I work as a Python developer in a very small startup. Sometimes, when making changes, I have to change several lines in several files. And moreover, there isn't any proper deployment practice/tool used here. So we just remember or note where we made changes, then copy paste the code into the GitHub repositories. Hence, I want to develop a proper deployment checklist/practice here.

How do you guys do the deployment at your organization? What tools or practices do you use, or sequence of steps you follow? Kindly comment down whatever you can to help.

Thanks