I had a similar problem & the fix was to loosen the pressure release screw & manually lift the motor all the way up and chock it with the holding mechanism on the T/T ----close the pressure release screw, then run the switch in the UP position for 5sec's, and if it does not lift motor off the chock, then open the fill screw & add fluid (then replace fill screw). Repeat this procedure until UP switch lifts motor off the chock. Stow chock & cycle the motor up/down with the switch button to insure you have full tilt & trim function.

You will also want to have your boat as level as possible ... I had to drop my tongue down as far as it would go with the 3rd wheel, as my boat sits in a parking space that's slightly angled towards the transom end.

My problem was lost fluid (my error) from loosening the release screw too far & blowing it out of the unit (along with a lot of fluid) when I was manually lifting the motor up to put it on the motor toter (to bring it home from storage bldg), as I had forgotten to bring a battery to do it "electronically". So don't loosen the release screw more than 2 full turns !!!
I tried several other methods to purge the air, most of them involved manually lifting & lowering the motor & checking/adding fluid ... but, all I got from those attempts was bruised arms & a sore back.

My T/T looks like this one :