In goalunited, the substitutions feature is currently being developed and tested from time to time within special united events in game. Once fully developed, this will be available in all competitions.
The complete formation has to be saved at least one hour before the start of the match.
At the moment, the only way to influence the match after this is to play half-time direction cards. Those can be played up to 50 minutes after the match has begun to react to an unsatisfactory first half.
Substitutions in matches are performed automatically only when there is a serious injury.
Info
In case of an injury sometimes the game may choose a better-suited player for that position even if the player is not on the same position as the injured player. For example, a Winger player enters the match instead of the injured midfielder.