If your loaded schedule has missing matches and all the teams in your division play each other twice or 4 times then this procedure will work for generating missing matches. It will not work if your teams play each other once or three times.
1/ Create your timeslots
Schedule > Scheduler Tools > Advanced Scheduler
In the advanced scheduler menu, 'Timeslots' tab, create the timeslots for the days - only create the number you need, no more.
From the advanced scheduler menu:
click on Reschedule
select the MISSING MATCHES
then submit the schedule
wait for it to finish and check it
then accept / reject