Unfortunately there really is not a way to help detect a pace to hold for your FTP test based on that 3 minute Vo2 max workout.
You can look at your past workouts and see if you hit any best 20 minute or 60 minute normalized power numbers. Typically we would get these from races or group rides, but those have not been happening.
You can also look at you average power for each set of the Vo2 max intervals (3 min ON, 3 min OFF, 3 min ON) which is 9 minutes so nearly half the field test. A lot of times I will give my athletes a 2 x 10 Full gas interval day the week before the field test to help determine a power target for their field test. But in the long run you still have to go off of feel. You should be rest and ready to put your best effort.
Best bet is to start your FTP test at 265 watts for the first 5 minutes let the effort come up to you and go from feel from there.