Add Delegates Access in Outlook

Open outlook

Click File

Click Account setting

Click Delegate Access

Click Add

Select the user to have Delegate permissions

Select what permission they have

Select if Meeting invites permission

My delegate only but send me a copy - Delegate had full control of meeting invites but you will get a copy, MAILBOX OWNER WILL NOT BE ABLE TO ACCEPT OR DECLINE INVITES
My delegate only - Delegate had full control of meeting invites, YOU WILL NOT GET A COPY
My delegate and me - both you and the delegate with get invites and be able to accept or decline them.

Click Ok

Delegate permission has now been set up