That depends on your weather. Impatiens do not like cold nights. Not sure where you live. If the night temps are above 45 degrees and days above 70 you can snip out the center of the tall and leggy impatiens shortening them by a few inches. This will encourage branching. If your nights are still cool keep the impatiens indoors at night but allow them outside under  cover during the day where they can get good sunlight. Leggy plants often suffer from lack of sunshine. You may need to wait until the weather is warmer and start with more compact impatiens as sometimes annuals that like the heat never get over the struggle they had when young and chilled.    Keep growing, Marianne Binetti