Do Triple Changers start the game in a specific Alt Mode or do you get to choose which of the two you start in?

They start in Alt Mode 1.

Source: Wizards of the Coast (2019-02-18)    【Link to Ruling】

Tags: Triple Changer

What are Triple Changers?

Triple Changers are characters with three modes: bot mode and two alt modes (labeled 1 and
2). They start in alt mode 1. When a Triple Changer flips, it can flip to either of the two other
modes.

Source: Wizards of the Coast (2019-03-01)    【Link to Ruling】

Tags: Triple Changer

If a card specifically says to flip a Triple Changer to alt mode, what happens?

If it’s in bot mode, you can flip it to alt mode 1 or alt mode 2. If it’s in one of its alt modes,
you can either not flip it or flip it to the other alt mode.

Source: Wizards of the Coast (2019-03-01)    【Link to Ruling】

Tags: Triple Changer

Can Escape Route be used on a triple changer in Alt 2 to flip into Alt 1 and vice-versa? Are triple changers affected by Roll-Out if they are not in bot mode?

Escape Route and Roll Out! convert characters from Bot mode to Alt mode. They cannot convert Triple Changers from one Alt mode to another Alt mode.

Source: Wizards of the Coast (2019-10-25)    【Link to Ruling】

Tags: Triple Changer

For Showing Off, can I flip Sergeant Springer to one alt mode and use its effect then flip to the other Alt mode and use its effect too? Or must I resolve Showing Off completely first?

Showing Off resolves completely before any abilities that triggered happen.

Source: Wizards of the Coast (2019-11-22)    【Link to Ruling】

Tags: Showing Off, Triple Changer