Ah. You’ll have to dig into your php admin to run some sql on your database. This is a little dangerous, so if you are not familiar with sql, it’s a good time to learn . First thing to learn is how to backup and restore from a backup. 🙂
For example: UPDATE xxx_newsletter SET followup= 1 where created > ‘2014-10-04’
xxx = the table prefix assigned to your install of wordpress.
…and the where statement can be used if you want to limit the update to only some users. But you could just set everyone to followup = 1 (Yes), then back in the wordpress screen, filter subscribers by ‘Unconfirmed’ and then bulk send the confirmation email.