The phrase "didst about face" is a somewhat antiquated way of saying "turned around." If you're looking for more modern and commonly used synonyms, there are several alternatives to choose from. One option is simply to say "turned," which is straightforward and universally understood. Another is "reversed course," which can be particularly useful in a metaphorical sense, such as when someone changes their mind about an issue. "Switched direction" is another good choice, highlighting the abruptness of the change. Lastly, "pivoted" can be a good descriptive synonym, used particularly when someone quickly turns on one foot to face in the opposite direction.