The best way to remove a hydrocolloid impression from the patient's mouth is:

Since alginate is a viscoelastic material, its tear strength is increased when the impression is removed along a vertical path with a snap. The speed of removal must be a compromise between a  rapid movement and a slower rate that is more comfortable for the patient. Usually an alginate impression does not adhere to the oral tissues as well as some of the elastomers do, so it is easier to remove the alginate impression rapidly. However, it is always best to avoid torquing or twisting the impression in an effort to remove it quickly. Specifically, the handle should be used minimally during breaking of the air seal (“suction”) or removal of the tray from the teeth. Phillips dental materials 12th edition page no 174