Can’t change format of a cell in Numbers on iPhone nor iPad

I’ve got a duration value in a Numbers sheet with an existing Automatic format. In this case, the value is the duration “23:57”. I want this to be reformatted as “23m 57s”.

Here’s my process that is NOT working:

Click the cell to be reformatted.

Click the Paintbrush icon.

Click Format.

Click Duration.

Uncheck Automatic Units.

Select Min Sec as the units.

Click Short as the format.

Click the Paintbrush icon.

The format does NOT change and it still shows “23:57” as the Automatic format.

This same behavior also happens when attempting to change the format of a whole column.

What am I missing? How do I change the Automatic format to a Duration format?

Thanks in advance,

Blaine