Did you use an ACTUAL retract servo?

Retract servos move 180 degrees and stop. Their movement must not be impeded nor must they hit any obstructions until they stop fully.

It could be you did not set up the retracts to permit full movement of the servo, so the motor stalled and burned.

If you did not use a retract servo, then your radio may have commanded the servo to move past the point the retracts permitted it to. An endpoint adjustment may have fixed this.

So remove the burned out servo. It sounds like you have a mechanical setup... so push the pushrods in and out and verify that the retracts work correctly.

Also note how MUCH the pushrods travel. You have to have the mechanics set up so that the servo only attempts to move the pushrods that amount, no less and no more.

Finally is the servo you replaced powerful enough for the job?

Too small of a servo may cause the servo to burn out as it can not produce the force required to move the retracts.