Missing Time Capsule Device in AirPort Utilities + Want Backup Mode Only
Until today, I was using a Time Capsule as a router and for automatic backups to Time Machine. I know, I know, it's old, but it'd been doing just fine and I didn't want to mess with it. Today, I purchased and setup a new router. Instead of the expense of a new external hard drive right now, I'd like to continue using Time Capsule for backups. I thought I was doing okay, but messed up and have now "lost" Time Capsule in AirPort Utility.
I connected the Time Capsule to the router using ethernet (LAN port to ethernet port). I then opened AirPort Utility > Time Capsule > Wireless Mode to "Off" and then Time Capsule disappeared altogether. I obviously messed up and chose the wrong setting. How do I find my Time Capsule again?! And what settings *should* I be changing to use it for backups only?