"Group" or "Grouping" Field

Using the tag panel I would like to edit or change the "Group" or "Grouping" field. However, I don't seem to be able to add that field. Can you direct me on how I might be able to do this? Sorry for this apparently very basic question.

Please note I have tried to use "Customize Columns" but there do not appear to be the appropriate name, value, or field options.

See the function Tools>Options>Tag-Panel for adding fields.
This is what the help says: https://docs.mp3tag.de/customization/tag-panel
To create a new field , select it from the field selection list.

The new fields are available in MP3tag V2.81 - so perhaps you have to update (according to your profile).

Many thanks the very quick and constructive advice. I have updated my version to v2.81.Indeed the "Grouping" field is now available in the dropdown selection of Tag Panel. "Grouping" was added to Tag Panel. Also the field is now available in Customize Columns, so I added a column as well.

I tried to update the "Grouping" of 128 files with the letter "E". mp3tag reported writing the new records. However, when viewing the column for Grouping, the updates do not appear. When viewing files individually in the Tag Panel, the filed does appear to be updated. When viewing the files in File Explorer or iTunes, the Grouping field is NOT updated for any of the files.

Much appreciate any thoughts or guidance.

The column definition should have %grouping% for both, value and field.

I doubt that the Windows Explorer shows this field.
How do you update the iTunes library? iTunes definitely does not do it on its own.

Here's the Windows Explorer view of mp3 file properties. Notice in the title bar it "Music Tools".

Sorry I wasn't clear. After updating the Grouping field with mp3tag, the update did not appear when I opened the files in iTunes.