For the second round, or any round after the second round, it should be the lowest rated player with the lowest point score. As the lowest rated player after the 4th round could have a 4-0. You would not give a full point bye to a 4-0 because the player is the lowest rated player. If the lowest rated player is 0-4, then you could give the player a bye. If he was the lowest rated player, without asking for a bye, he would have gotten a bye in the first round.
a)Re-do the pairings?
Since the player did asked for a half point bye in round 3, the pairings are in error. If the player did play in round 2, then had an 0-2 as the lowest rated player, would have gotten a bye in round 3.
Since not knowing who had a bye in the first round, it would be the lowest rated player. Players that are new or unr will not get a forced bye as its important to get new or unr a rating out of the event. If the lowest rated player is 0-1, and the second lowest rated player is 0-1 also. If it is save to say both players would lose the second game, it only would change the bye one round difference. As the player did ask for a 3rd round bye, only change the bye from the person having the bye in the 3rd round, to having the bye in the 2nd round.
If the second lowest rated player, did go 0-1, 0-2 and 0-3. The second lowest rated player, just change having the bye from the 2nd round to the 4th round. As the pairing was not changed, and only if the second lowest player was 0-3 for the 4th round pairings.
Taking what could have been, its’ only in theory as I have not looked at the crosstables. Even if I did, making a claim of who should have had a bye and who should not would not be fair. As the TD should use the official ratings not the web ratings. Second the web rating can be higher or lower then the official rating, making a claim on pre-rating would not help.
If the player is the lowest rated player, and was not given a bye in the first round. As the player asked for a bye in round 3, then the TD did not give the player a bye in round 1, as the player asked for a round 3 bye. It looks like the TD forgotten the requested bye in round 3, for the pairings in round 2. As the TD did recall the requested bye in round 1, as he did not give the bye to the lowest rated player during round 1. As the bye was requested for round 3.