do i just put it in the brahma folder?
and i rename it?
OK, so you followed the guide here then?
https://github.com/Plailect/Guide/wiki/Part-5-(arm9loaderhax-&-Cakes)
If you followed everything you should have a9lh installed to your system and BootCTR9 installed. Did you put the boot_config.ini on the root of your SD card along with the arm9loaderhax.bin and arm9bootloader.bin they told you to install? Did you make a folder called a9lh on your SD card and stick the Uncart.bin file there? Just making sure.
If all of those things are true, it should boot Uncart very reliably when you hold B on boot (hold it before you power on to make sure you get it fast enough). I have something similar set up myself, so I know it works if you're set up right.
*edit*
By the way, a note on loading the regular Brahma version of Uncart...yeah, you're not the only one who has had trouble with it. I had to try it a ton of times before I could get it to load. The loading of it is unreliable for some reason (not so for a9lh though, just the Brahma version).