Here's how it works:
There is a maximum amount of any substance that a certain amount of solvent can hold in solution. When it is at this point it is known as a saturated solution.
Hot solvents have a higher maximum than cold, it's one of those facts of chemistry / physics.
It follows that cold solvents have a lower maximum than room temperature.
Specifically, room temperature ( 20C) naphtha can carry nearly 3g of DMT per 100ml, and freezer temp ( -20 C ) naphtha can only carry about 100mg in 100 ml.
( see here:
Chemical Guide to classic Psychedelics (DMT, 5-MeO-", Mescaline, Harmalas, Salvinorin A, ...) )
So if you have more than 100mg of DMT dissoved in 100ml of naphtha at room temperature, then putting it in the freezer will mean that excess DMT will crystallise out of solution and coat the walls of whatever vessel you have.
If you were then to let the naphtha warm up again the DMT would dissolve again. So the cold naphtha is poured off before it warms up, leaving crystals to be scraped up after any left over solvent has evaporated.
The advantage of this over evaporation is that only DMT gets left in the dish, any impurities that are soluble in cold naphtha ( like plant fats ) get poured out.
The procedure is best explained, with pictures, from step seven onwards here:
Cybs' Hybrid ATB 'Salt' Tek - DMT-Nexus Wiki
Good luck!