Here are two videos I posted on TikTok using a certain method of addressing a tongue that likes to pull back. Use of this exercise can assist in keeping the throat open and keep the tongue from shutting throat space. I also do go into the necessity for proper guidance with this exercise and caution against doing it at all if it feels like there is too much resistance at first.
If you try what is in these two videos and find it is just too difficult and the tongue is truly very tense, then just hold your tongue outside your mouth for roughly 30 seconds at a time a couple of times a day. Over time it will start to relax more and then you can try one of the suggestions in these videos.
As always, ask me questions if you don’t understand it or seek the advice of your personal trusted vocal professional.