If my opponent has Carrion Dredger in his base and I play Repeated Bellows, can I kill the bird token after with the second trigger of Bellows?

No, you cannot kill the Bird token created by Carrion Dredger with the second execution of a repeated Bellows Breath in this scenario.

Reasoning

1. Timing of Choices: According to Rule 820.2, when you pay the Repeat cost for a spell, you must make all choices for both the initial execution and the repeated execution at the Make Relevant Choices step of playing the card. This step occurs when the spell is being played, before it is finalized on the chain.
2. Targets Must Exist: Because you must choose all targets for both instances of the effect at the time you play the spell, any unit you intend to target must already be on the board at that moment.
3. Interaction: When you play Bellows Breath with Repeat, you choose your targets for the first and second executions upfront. The Bird token created by Carrion Dredger does not exist when you are making your targeting choices; therefore, it cannot be selected as a target for the second execution.

Sequence

1. Play Phase: You announce Bellows Breath, choose to pay the Repeat cost, and declare your targets for both the first and second executions.
2. Finalization: The spell is placed on the chain.
3. Resolution: Bellows Breath resolves. It executes its first instance of damage, then its second.
4. Deathknell: Because your targets were locked in during the Make Relevant Choices step of playing the spell, you cannot retroactively choose a unit that enters play as a result of the spell's own resolution.

Note: I could not fully verify this ruling against the retrieved rules.