Just cut off the dead brown branch. Leave the alive one alone to rebuild the plant.

Agree, cut of the dead branches all the way down to the base, so it can’t harbor pests. The green shoot and the rest of the plant are probably fine.

After you cut off the dead branch (try not to leave a stump), leave the rose alone, except for water, for a few weeks. It may "just sit there" for while, because it will be growing roots under the ground. I would not give it any more food, or spray it with anything - it just needs to recuperate from being planted.

Jackie