Missing 'Auto Delete Conversations' option on iPhone

In Settings > Apps > Messages - Message History - there are 3 options - 30 days/1 Year/Forever

What do you have checked there? Either way if you deleted a message, it can only be retrieved if it was deleted less than 30 days ago, by checking the recently deleted folder. If it's there, it can be restored. If it's not there, it can't be restored.

You could always ask the other person in the conversation to send it back to you.

Again, if they aren't in the Recently Deleted messages folder, they are GONE.

claubyr wrote:

in iPhone storage I accidentally check delete old conversations. I wasn't able to uncheck late and now it's gone. Help

That is something different. As has already been pointed out, if you did that an they aren't in recently deleted, they are gone forever.