**The Problem:** My macOS partition doesn't appear as an option at boot 

**Background:** I had a main el capitan partition and a bootcamp partition. I used the EaseUS program to resize the bootcamp partition from 90GB to 45GB and after rebooting, I could no longer see any option but 'Windows' when holding <kbd>alt</kbd> at boot.

**My Initial Investigation:**  I took a look at my paritions in three different places: The EaseUS program, `diskpart` on windows, and the disk utility on macOS Recovery Mode.

On both EaseUS and `diskpart`, my partitions look fine:
[![EaseUS][1]][1]
[![diskpart][2]][2]
However, in disk utility in recovery mode, it looks a bit different. On the sidebar I can only see one child partition of the SSD (BOOTCAMP). However when inspecting the disk, it shows three partitions (Untitled : 145.36GB, Untitled: 650MB, BOOTCAMP: 48.32GB) and a 'Child count' of 4. I wish I could provide a screen shot, but AFAIK this is not possible with recovery mode.

I also ran first aid on the SSD from disk utility and everything verified as OK.

**Additional Comments:** I'm a bit out of my depth here  and would really appreciate any advice as to how I can boot into macOS again

**Edit #1:**

In response to @DavidAnderson
I am using a an early 2015 13" Retina MacbookPro (MacbookPro 12,1).

My Volume 2 details are as following:

    Partition 2
    Type    : de94bba4-06d1-4d40-a16a-bfd50179d6ac
    Hidden  : Yes
    Required: No
    Attrib  : 0000000000000000
    Offset in Bytes: 209735680
    
      Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
      ----------  ---  -----------  -----  ----------  -------  ---------  --------
    * Volume 2         Macintosh H  HFS    Partition    135 GB  Healthy    Hidden

And my volume 3 details are:

    Partition 3
    Type    : de94bba4-06d1-4d40-a16a-bfd50179d6ac
    Hidden  : Yes
    Required: No
    Attrib  : 0000000000000000
    Offset in Bytes: 145570975744

      Volume ###  Ltr  Label        Fs     Type        Size     Status     Info
      ----------  ---  -----------  -----  ----------  -------  ---------  --------
    * Volume 3         Recovery HD  HFS    Partition    619 MB  Healthy    Hidden



**Edit #2:**

I was able to fix it with the accepted answer!

I used gdisk and the `t` command to set the GUIDs as recommended and then used the the expert command `a` (expert commands are accessed with `x`) to set the attribute field #49 to get the attribute value recommended. Works perfectly now!

  [1]: https://i.sstatic.net/xKwdy.png
  [2]: https://i.sstatic.net/YFY8t.png