Select a message from the dropdown list.
It can be an active or inactive message, it does not matter.
Once the message has been selected, it will automatically fill the subject,
message, attachment, SLURL, message settings and the IM message

It will also select all the groups you checked before you saved your message.

You may need to look at the groups lists though in case your bot has joined
any new groups.

Notice button:

Clicking on this button will send your selected message as notices to
all the groups you selected from the Notice groups box.

IM button:

Clicking on this button will send your selected message as group IM's
to all the groups you selected from the IM groups box.

Both button:

Clicking on this button will send your message as both notices and
IM's to all groups you checked from both group boxes.