Complex sentence: In June 1997 Cookie Jar, a competitor with about 30 outlets, was purchased by Millie's Cookies and its stores rebranded, before Millie's itself was acquired by Compass Group in 2003.
Split into simpler sentences: In June 1997 Millie's Cookies purchased Cookie Jar, a competitor with about 30 outlets. The newly bought stores were rebranded as Millie's Cookies, before Millie's itself was acquired by Compass Group in 2003.