Sign in to your PSN account on the PS4
Go to Settings
Select Account Management
Select Activate as Your Primary PS4
Choose Activate
Sign in to the other PSN account on the same PS4
Open the game library or PlayStation Store
Download the game on the other account if it is owned digitally
For disc games, insert the disc to play on the console
Keep the primary PS4 activation enabled for game sharing on that console
Make sure both accounts stay on the same PS4 for access to shared games