Agonizing Blast states -

"Choose one of your known Warlock cantrips that deals damage. You can add your Charisma modifier to that spell’s damage rolls.

Repeatable. You can gain this invocation more than once. Each time you do so, choose a different eligible cantrip."

However, you are unable to choose this option again after selecting it the first time. That is all, have a tight day.

Known issue.

 From the official Player’s Handbook - Issues and Support Thread

Quote from PrincessPastelf >>

Warlock

Warlock Invocations. There are a number of Warlock Invocations that are currently unsupported:

• Agonizing Blast - This is currently only supported for the Eldritch Blast cantrip.