Generally, the first step, in reconstructing messed up the partition tables, is to dump the current contents.
If running High Sierra (macOS 10.13), you would need to boot to internet, internal or USB based macOS Recovery. The following commands would partially dump the contents of the GPT and MBR partition table.
gpt -r show /dev/disk0
The partition tables can then be repaired by using a variety of tools. A well known third party tool is gdisk.
Since you can only boot to Windows, the
fdisk commands would be unavailable. There are third party Windows equivalents named
readmbr.exe that can dump the contents of the partition tables. The syntax for executing these commands is shown below.
Note: These commands have to be run from a "Administrator: Command Prompt" window.
Additionally, the following command will dump the GPT attributes.
There also a Windows version of the gdisk command. Below is the syntax for executing this command from a "Administrator: Command Prompt" window.
If you have trouble using the
gdisk command, you can post the partition table information in your question and ask for help.