The healing process is automatic for all injured players with 40 years old or less. Starting at 41 years old an injury will always be infinite and a bruised condition will last until next year when it will progress to an infinite injury.
The treatment is applied every day and the health is recovered by a constant value given by the player's age and modified by medic levels.
In order to get a good result from this tool the data used must have good quality which means avoiding TSI's changes from training or skill drop by age.
The best source before the injury is the last match played with full health and you can find it at player's performance history.
The best source after the injury is the player's current values one day after the match where the injury happened - if a long time has passed and you don't have this data then you should use the first match after the injury at player's performance history.
Please remember that an injured player can't play while a bandaged can but with a penalty over the performance.