How to format text in text area column?
This page describes how to format the text in a text area column type.
You can format the text in the text area column using the wiki markup.
Check the use wiki markup checkbox in order to enable the editor. It allows you to add formatting to the column such as italics, bold, underline, alignment, or color.
Check the full list of the text formatting in the Atlassian documentation
The editor will be available every time you add value to the textarea column.
Make sure Wiki Renderer is enabled in your Jira.