How to Modify a Reconciled Txn?

[jcard21 xxxxxxx]

I'm using Windows Vista / gnuCash 2.2.9

I cannot for the life of me figure out how to modify a reconciled txn.
I'm trying to add my bank's confirmation number (alphanumeric) to the
NOTES field. I'm not changing amounts or dates.

I've looked through the Edit/Preferences ... I didn't find anything related.

Can someone spell out how to do this?

Thanks!

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jcard21