Manage saves and add-ons. Add-ons are no longer in ready to install section.

You can find obtained add-ons on the game management page

Or you can find these in MS Store

Make sure the season pass is installed on your xbox one, you can check by going to the manage game section of Bioshock infinite (press menu button on controller when Bioshock infinite is highlighted, and select manage game & add ons) If it's not installed,
then select the season pass from the ready to install and install it. Then start the game, on the game menu goto the add-ons, and select each add on. This should bring up the Xbox 360 store, and you can then select each add on to download. Make sure that it
states that the add-ons are free otherwise you will be charged for them. You will get a message off the xbox one stating that each dlc will be placed in the games ready to install section. So go back the manage game section of bioshock infinite and install
each add-on. Once you have done that, you will be able to play them.

If digital they will be in ready to install, if on disk install the game and then go manage game and install any add ons, games saved to cloud will sync automaticlly

Have you highlighted the game and pressed the menu button and opened manage game & add ons and checked in the ready to install section of the game.

if you click the pause button when hovering over fo4 there should be an option to manage game and add ons, check in the ready to install section.