So think about what "subtle" means to you. Some synonyms are delicate, inconceivable, elusive, ephemeral, quiet, small - just like pick one.
Then pick of an element, elements are very like archetypal, so they resonate very deeply in our psyche. These things have been in our collective consciousness for idk like hundreds of millions of years at LEAST: theres Earth, Air, Fire, Water, Space, Electricity, uhhhh yeah. The element spirit controls the other elements - thats you.
Now imagine that element is as subtle as you can imagine it being, we're gonna use our imagination now. Whatever you image subtle water or subtle fire being like, run with that and imagine it as much as possible. If you cant do it visually in your head, ive seen people use drama or drawing or writing or speaking or imaginative feeling(rather than visual), just whatever works for you to raise the energy. Raise the energy.
Imagine some source of this energy like the sun or the ocean and imagine directing this subtle elemental energy into yourself, again either visually in your head or via drama or writing or hand gensture, or literally anything, just get the channel flowing. Raise the energy, raise the energy.
You can localize the endpoint to a part of your body or psyche or soul or whatever that you want to heal, or someone else or a collective. Might want to get permission first though.
This "subtle" energy will raise the frequency of what you work on it with. Which can be painful or disorienting, or relieving or elating, but it's spiritual purification. Not necessarily a good thing, but can balance spiritual distortions.