Hi, msstas, welcome to the forum!
I'm sure your trailer has electric brakes, but they may not be working. If you look behind a wheel, you should see two wires going into the back of the wheel. That is the electrical supply for the brakes.
The easiest way to see if they are hooked up and functioning, in my opinion, is to jack up one side of the trailer (put the jack on the frame next to the axles, not on the axles themselves) or use one of those ramps that you can drive one of the tandem wheels up on so that the other hangs free. Then, spin the free-hanging wheel(s) by hand. They should turn easily with only a small amount of noise. Next, pull the breakaway plug on the tongue, which should connect the trailer battery directly to the electric brake(s) on the free hanging wheel(s). Now the wheel(s) should not rotate at all.
Re-innsert the breakaway plug so that your battery is not drained and do the same test on the other side of the trailer.
If a wheel is very noisy or it feels like it may be binding a bit with the brakes off, you may have a brake that has fallen apart in the wheel (I had this happen twice), or, you may have bad bearings. Either one needs to be addressed before you try to tow it again.
If the wheel continues to rotate easily with the breakaway plug pulled, the electric brakes are not working. Possibly, the wiring is disconnected, or, they may just be worn out or broken. Again, you need to fix this before using the trailer.
Electric brake assemblies are not particularly expensive or difficult to install. I've replaced the ones in my trailer myself. And, I inspect my brakes when I service the wheel bearings. I got this kind: 10" Nev-R-Adjust Electric Brake Assembly for 3.5K Axles - RH Dexter Trailer Brakes 23-469
If your brakes seem ok using the tests I've described, you possibly need to adjust the "gain" or current that the brake controller is supplying. You want to feel the brakes grab at a speed of about 25 mph on level ground but you don't want the wheels to lock up. Ideally, if you've adjusted everything right, stopping should feel about the same whether you're towing or not.
And, it's possible your brake controller is not sending current to the trailer brakes. That circuit is fuse protected in your tow vehicle, and the fuse can blow.
Hope these thoughts help.