Is this a cassette dump file, cartridge? if so, I would assume you would load games the same way as the original computer system.. some form of LOAD command.. I'm not familiar with the Ti-99 as I was a TRS-80 kind of guy when growing up... but you may find the manual online somewhere.
2 games were included with the emulator = moonpatrol.ctg and I think the other is shootout.ctg. Both have basic option 1 and 2. When I choose option 2 the games boot up perfectly. I could not find any clues as to what was done to get option 2 per game/folder inspection. It is just there in .ctg format in appdata>TI99>cart.
Tried putting other games in same spot but again just basic 1 option.
I did type in some suggested commands via website but with no luck.