I was also informed when I first started out by my lfs that 2 damsels would cycle my tank and get along.
They both died within a week, and I learned about phantom feeding and shrimp.
I'd continue coming to the forum for help in future before doing anything ^^
If you want to save your fish, 1. I'd consider asking your LFS to hold them for you while your tank cycles
2. Make a quarantine tank and keep them in there, with daily water changes about 30-50% and maybe add prime just in case.
3.wing it see if they live or die, you can also dose prime to your tank. It makes ammonia, nitrites, and nitrates " invisible" for I believe 48 hours.
Invisible meaning, they won't harm your fish during the time, but still exist, and will come back after that time has passed.
Or... you can have a fish cycle, let them die and wait for the tank to cycle and try again..