How could I access dark energy/Matter and transfer it to a crystal to store it?
I’m afraid the answer is, you probably don’t.
This was only ever a hypothesis, and is reaching the end of it’s course - they’ve been looking for dark mater/energy for over a decade, and there has been no evidence yet. They have found sources of “missing” matter that they thought wasn’t here before. Meanwhile other evidence they hoped to find has been proven not to exist. WIMPS don’t exist, for example. Other systems “break” he dar mater model.
Basically there is mounting evidence that this model is defunct. It’s a pity and I rather liked it as well, but if it doesn’t work, it doesn’t work.
Having said that, you can use your mind t intend to store any kind of energy you like. Energy will flow based on your intent and something will happen. People ‘charge’ crystals with moonlight and incense, I’m pretty sure you can make up whatever you want.
What result are you looking for? Maybe people here can make suggestions for what worked for them.