docs: Add unmerge issues text (#4245)

* docs: Add unmerge issues text

* Update src/docs/product/sentry-basics/guides/grouping-and-fingerprints/index.mdx

Co-authored-by: Isabel <76437239+imatwawana@users.noreply.github.com>

Co-authored-by: Isabel <76437239+imatwawana@users.noreply.github.com>

Author: t-h-man

src/docs/product/sentry-basics/guides/grouping-and-fingerprints/index.mdx

@@ -59,6 +59,8 @@ You can also do this from inside a single issue. Click the Similar Issues tab
 
 **Warning:** Future issues will get added to the merged set only if they match one of the stack traces in the merged set.
 
+If you'd like to unmerge issues, you can go to the **Issue Details** page and click the “Merged Issues” tab. You will see the fingerprints that have been merged into that issue. Select the appropriate checkbox(es) and click “Unmerge”.
+
 ### Fingerprint Rules
 
 Here's an overview of what we'll do using **Fingerprint Rules**