Choose a key, the entry point, there are many options.
Breath is a common and good one. All require tenacity and practice.
Here is a suggestion from Eric Harrison.
"Breathe in deeply, opening the ribcage.
Sigh: let the breath go without forcing it.
Rest in the pause, feeling the belly soften.
Wait until you really need to breathe in again.
Take a second big in-breath.
Feel the chest open further.
Drop into the soft, loose out-breath.
Pause again and wait.
And a third time, feeling everything loosen.
Let your breathing resume its natural rhythm.
It will now feel slow, deep and soft.
Breathe naturally or sigh gently as you wish.