Zoom Video Communications Inc ZM.O jumped 4.8% after raising its full-year profit outlook on strong enterprise demand. By Devik Jain and Anisha Sircar May 24 (Reuters) - U.S. stock indexes were set to fall on Tuesday following a strong relief rally in the previous session as weak forecasts from firms including Snapchat owner Snap Inc added to nerves about an inflation-struck economy. Snap IncSNAP.N plummeted 33% in premarket trading, dragging down several social media and internet stocks, after the company slashed its second-quarter earnings forecast and said the economy had worsened faster than expected in the last month.