Images appeared to show Drissa Traore, Brandon Ormonde-Ottewill and Jeremy Balmy taking the legal high, commonly known as laughing gas, via balloons.
Swindon suspended the trio on 7 April and, following a club investigation, a statement said: "Swindon Town now consider this matter to be closed.
"The three first-team players have been fined for their actions."
The statement added: "The trio acknowledge that their actions were wrong and would like to apologise to their team mates, the club's staff and the supporters.
"They are keen to move on from this issue and get back to training to help the team as quickly as possible. All three will be considered for selection once again this weekend."
Head coach Luke Williams told BBC Wiltshire: "They will be available (on Saturday) because they will have served their suspension time but the boys will have to earn their right to be back in the matchday squad.
"I should think there's a level of conditioning that they've now lost because they have not been training for a fortnight, so they'll have to be re-conditioned.
"They'll have to show in training every day that they're desperately trying to make up for what they've done."
Swindon host Chesterfield in League One on Saturday.
Swindon Town have fined three players after they appeared to inhale nitrous oxide in a live social media video.