How to Map "Written By" to Composer

Discogs doesn't use Composer for their Metadata tag but instead uses Written By.
How do I map this?
Is their anything I might be missing as a newbie to this?

You could check the extended tags Alt+T whether you find COMPOSER there or Written by.
Also, there is a setting for mappings, see the options Ctrl+O > Mapping

The extended tag is Composer..

Yes and I don't understand how to use it.

Isn’t this what you wanted? If the extended tag panel shows the data is being stored in the Composer tag field, there is nothing to remap.

Then have a look at the documentation about how to customize tag panel and file list:

What I need is another map for Written by to Composer

In the page Mapping, it begins with

Mp3tag displays tag fields either directly with their corresponding name from the files (e.g., for files with APEv2 tags like Musepack or VorbisComments like OGG and FLAC). I don't know what a discogs file looks like, but I know their display is "Written By" and that is very different from WRITTENBY.

The mapping in "Options" also doesn't help since it uses in this order: VorbisComment TRACKNUMBER TRACK.
So, I'm not using VorbisComment, I'm using discogs and that isn't in the list of fixed mapping. What do I put in that field?

Finally, in the first page mentioned, it explains how you work with your files to translate them into Mp3tag format or Id3v2 format. I don't have a file as I'm looking at what discogs displays and importing that into my file.

I also assume that I can put written by into Source and target is composer. Note: I didn't try to capitalize to make no assumption about what it'd look like. I also assume I have put them in the correct position, based on what I saw in Options, but I'm not always good with logic.

What could be

if the data is already stored in COMPOSER?

Please post a screen shot of the Extended tags panel Alt+ T with one of these files so we can see an example of what you mean.

I just saw your posts but am adding to my above post with this.
The web page source for a "Written By" reads as
and it doesn't even mention "Written By"

Track 1png

I think you are asking if I have a composer field, which I don't.

Apparently you use a web source script.
If you want to get data from something that is labelled "Written by" in Discogs, you have to adapt the web source script to do so.
This has nothing to do with the mapping in the options ...

So please us a search to look for how to get composer from discogse, e.g.:

Thought I'd done that but I was probably looking with mapping alongwith composer so it would not show.

At least the Discogs-Websource script that is included in Mp3Tag does not fetch any composer-info.
There are other websource-scripts (Deezer, Apple) that can do that but the sources do not have this information for every album and the information is not 100% reliable. Sometimes the composer stands for composer and lyricist.
If you don't know how to install these scripts: