You can either buy a 5/5 Egg off another Tamer
You can try and hatch the DigiEgg:
Insert 5 sets of required Data without the DigiEgg breaking.
The process is delicate and not a 100% guarantee, but it is well worth the effort because the Mercenary Digimon, when hatched, will be larger with better stats than if it were to have been hatched as a 4/5 Mercenary Digimon, and subsequently, a 3/5 Mercenary Digimon.
If the DigiEgg breaks at any point during the Data input, you will need to start over with a new DigiEgg and new Data.