1. Core wallet
2. Help
3. Debugwindow
4. console
5. importprivkey "digibyteprivkey" ( "label" ) ( rescan )
Thats my best guess!
tested this recently but with a dirty copy of the new 6.14.1 wallet, the format of step 5. was just
importprivkey
The wallet seemed to hang but process was busy and I left it alone, came back a while later and it had been completely successful.
Yep, importing private key can really takes sometime while the wallet thoroughly scanning each transactions in the blockchain.