How to give someone access to your Calendar using Outlook app
Open the Outlook app & choose the Calendar
Click on your profile top left
Go into Calendar settings
Choose Add People
Type the name of the person to search
Once selected use the Arrow to continue
Click on the > to add permissions
For delegate access to input you probably want to choose ‘Can Edit’ & ‘All Details’
Once permissions are selected go back and use the tick to finalise