The first thing is to determine what type of fiber is connected between the buildings. The two common types are singlemode and multimode. Singlemode usually has a yellow jacket. Multimode will be either orange or light blue. It's possible that the jacket color is different but it's a pretty safe bet. To be sure look at what you ordered from the fiber vendor. Is this your own dark fiber or are you leasing a circuit from a carrier?
Once you find out what kind of fiber you have, you'll need a transceiver for each end. These are called "SFP" for Small Form Pluggable. It's about the same size as a pack of gum and slips into the rectangular fittings near the right side of the switch. These are shared ports. You can either use the SFP or the adjacent RJ45 but not both at the same time. You want gigabit transceivers for either singlemode or multimode depending on your fiber type. Singlemode transceivers can be ordered for use on long distances (80 KM or more). You don't need or want to get long-reach transceivers unless you are actually going those longer distances. They cost more and have more powerful lasers which can overload the other end on short-distance links.
A little secret about transceivers. SFP is a recognized standard and about 90% of the transceivers in the world are made by a company called Finisar in China. Standard gigabit transceivers are very inexpensive. Inside the transceiver is a small ROM that has a serial number and brand information. Companies like Adtran and Cisco buy transceivers from Finisar, have their brand set into the ROM, and put a sticker with their brand on them. They then sell these for many times what the exact same transceiver costs generically, issuing warnings about the terrible hazards of using "non-Genuine" optics. The only real hazard is to the shareholders who don't get the insane profits. You shouldn't pay more than $30 for a multimode transceiver or $50 for singlemode. You can get generic transceivers coded with the Adtran or Cisco ROM for a small fraction of the cost of "genuine". Adtran singlemode is 1000-base-LX part number 1200481E1. Adtran multimode is 1000-base-SX, part number 1200480E1. Google the Adtran part number, check with Fluxlight or any reputable optics vendor for a compatible.
Next you'll need jumpers at each end matching the type of installed fiber to connect to your router. Fiber typically terminates in a junction box or patch panel and you'll need to extend this to the router itself. You'll need to look at the junction box or panel to determine how it's terminated. It will usually be on one of three types of connectors, as follows:
SC - "Stab and click" - about 1/4 inch square connector. Jumper is pushed in and clicks. May be grouped in pairs.
ST - "Stab and twist" - about 1/4 inch round connector, has a bayonet type fitting. Jumper is pushed in and turned to lock in place. Typically found in older installations.
LC - "Little click" - about 1/8 inch square. Usually grouped in pairs. There's a tang on one side that latches it in place, similar to a telephone or Ethernet modular jack. This is what connects to the transceiver, and it may be on your patch panel as well.
The router end will be "LC", so get either singlemode or multimode jumpers to match your installed fiber. One end of the jumper will be LC and the other end should match your patch panel. These are typically sold in metric lengths. You'll want some slack, fiber cable should have gentle bends. Tight kinks will break the internal fiber.
Each connection takes two strands of fiber, one for each direction of transmission. If the link doesn't come up, it may be because both transmit strands are facing each other and both receive strands are facing each other. Swap the two strands at the patch panel on one end.
Last, you'll need to move whatever interface configuration is on your T1s to the ports connected to the fiber.
TL;DR:
Find out what kind of fiber you have.
Buy Adtran-compatible gigabit transceivers to match the fiber type.
Buy jumpers of the correct fiber type to connect your transceivers to the patch panel.
Reconfigure the devices to mirror the T-1 link
If link doesn't come up, swap the fibers on one end.
