How to delete a partition

You did not remove the Boot Camp partition correctly. You need to do the following:

Internet/Network Recovery of El Capitan or Later on a Clean Disk

If possible back up your files before proceeding.

1. Restart the computer. Immediately after the chime hold down the (Command-Option-Shift-R) keys until a globe appears.
2. The Utility Menu will appear in from 5-20 minutes. Be patient.
3. Select Disk Utility and click on the Continue button.
4. When Disk Utility loads select the drive (usually, the out-dented entry) from the side list.
5. Click on the Erase tab in Disk Utility's main window. A panel will drop down.
6. Set the partition scheme to GUID.
7. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
8. Click on the Apply button, then click on the Done button when it activates.
9. Quit Disk Utility and return to the Utility Menu.
10. Select Reinstall OS X and click on the Continue button.

Note: This will install the version of macOS that was originally pre-installed. You can then upgrade it by downloading the Mojave installer from the App Store: Get MacOS Mojave now from the Mac App Store.

Hi,

You can delete bootcamp partition with Bootcamp Assistant.

The following document could help your question.

https://www.macworld.com/article/1156195/mac-apps/delete-boot-camp.html

No. You don't need to do that. But if you have not restored the other partition then you are installing macOS onto the first or Mac partition.