“帮我推一下门” is wrong. "帮我推着门" is correct. verb + 一下 means the action is done in a moment. verb + 着 means the action is kept doing for a while. "帮我hold住这个门不让它关掉" means that "keep the door open", so you must use verb + 着.

帮我扶一下门

帮我顶下门 帮我扶下门

地道的汉语，应该说“帮我顶住不要关上”

帮我扶着门，不要让它关上。