I tried a few ways, but I couldn’t get it to reset and let me back in to change it manually. Checking back on it now, the text has reverted to its default text but with the raw variable (so no ‘revert’ option available) and trying to edit manually throws the 500 error. I also tried the safe mode workaround for the other topic, which didn’t seem to have any effect.
Searching for js.chat.retention_reminders.dm in English (UK) locale gives me three choices, but in Español it only offers two.