The bootcamp assistant is not letting me advance after I press "continue"

So recently I reset my Mac to factory settings and now I want to delete windows but when I press continue in the bootcamp assistant this shows up:

The startup disk cannot be partitioned or restored to a single partition.

The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows.
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I already tried the command + s thing and I can't find any "disk0s5" or whatever in my partition tab

Can someone help me out step by step?

You should have deleted the Bootcamp partition prior to resetting your Mac. You may need to start up from another drive to partition and wipe your internal drive.

What Mac model and year are you using? Can you access internet Recovery? Read through this Apple Support Document, https://support.apple.com/en-us/HT201314.

ferrarr said:

You should have deleted the Bootcamp partition prior to resetting your Mac. You may need to start up from another drive to partition and wipe your internal drive.

What Mac model and year are you using? Can you access internet Recovery? Read through this Apple Support Document, https://support.apple.com/en-us/HT201314.

Click to expand...

iMac (21.5-inch, Late 2015)

What is internet recovery?

Internet Recovery is where your iMac starts up from Apple servers, it is a different key combination than the Recovery partition. Have a read of my link. Look at the section "If you can't start up from Recovery". I know you ca start your iMac, but you need to boot off a different drive to erase the internal.

Do you have a backup of your system, either Time Machine, or a clone?
Or, do you have a bootable USB installer?