Want to delete UBUNTU 18.04 LTS from MacBook Air 2017 model

I'm completely new to using a Mac, and recently installed UBUNTU by following some YouTube videos and it worked fine. I added 50GB for the UBUNTU partition and 8GB for the SWAP partition. I now want to restore my 58 GB back to the MacOS partition and want to delete UBUNTU.

Can someone please give me a detailed step-by-step process on how to delete UBUNTU and reFInd and retrieve my MacOS back completely. Since it's a new Mac, I'm not worried about data loss and there are no important files.

Just perform an erase install. Boot to macOS recovery and then repartition the whole drive and the installer downloads from the internet.

• How to completely reinstall Mac OS X?

My answer here works best if you use internet recovery so you don’t need to mess with making a bootable usb and then get to recovery.

• https://apple.stackexchange.com/a/315885/5472

In addition, there is no benefit to using a bootable USB or local recovery partition over just using internet recovery unless you already have the installer downloaded or a bootable Mac spare and handy. See About macOS Recovery for details.