Ok, thanks for your hints.
Another hint, open two browser windows, one regular one incognito, log into both airlines, recreate the flight plan, same times, don’t worry about slots if they are red, just finish the second flight plan, after you are done, lock the first flight plan, if you had any red slots on the second flight plan just move the flights on the first flight plan to a different time of day for a period of 3 days while locked and then delete the flight plan after 3 days. If it is not possible to move those flights from the first flight plan to other times, then just delete the first flight plan. Then go to the second flight plan and click edit on any of the red flights with red slots, and save, all red flights with red slots will now be yellow, activate the second flight plan with 3 days delay.
Rinse and repeat.