Just tap on the runner and you will get a list of players on the roster. Select one of them and that player will replace the runner.

For a more precise interpretation, MLB Rules 9.12.a.3

(a) The official scorer shall charge an error against any fielder:

(3)

• when such fielder catches a thrown ball or a ground ball
  in time to put out the batter-runner and fails to tag first
  base or the batter-runner;

Given your description, it is an error. Not having your foot on the bag is a physical misplay. You could call it a mental error, but it was the physical act of putting the foot down off the bag which makes it an error. E3.

The umpire is in the infield between 2nd and 3rd not out in the outfield grass / edge of infield. It’s my understanding if it hits the umpire in that field location it’s a live ball. However if it hits umpire in the infield it’s a dead ball - batter gets a hit and runners advance one base. Is that ...

Unfortunately, you can't always determine earned/unearned at the time the run scores. This type of editing would have to be done after an inning. Right now, the only solution is to edit the stats to get them correct. You can't directly edit the status of a particular run. It has been mentioned befor...

Just for backup for those interested, per MLB 2018 Rules 9.15(b): When a batter leaves the game with two strikes against him, and the substitute batter completes a strikeout, the official scorer shall charge the strikeout and the time at bat to the first batter. If the substitute batter completes th...

Well, it is always difficult to interpret a judgement call like offensive interference without seeing the play. If the ball was hit like you say in that it would have been judged a base hit even without the runner interference, then it seems like the umpires made the correct choices in placing the r...

Also, scoreboards can be difficult to interpret. Was the E3 shown the scoring call on the batter or just that an E3 occured (which is what you have scored for the runner)?

Yes. I think this suggestion has been made multiple times.

Good question. I'll have to look this up when I get a chance. My first inclination would be that this is an error since the fielder is in charge of his glove. A ball shouldn't get stuck in most gloves (since we don't see it that often).