Little bum bums sleeper question!

Alicia

Does anyone possibly know what I need too do too fix the zipper on a little bum bums sleeper? It’s got the two way zippers on it but when zipped it doesn’t stay shut it just opens. The sleeper is used I purchased it from someone unaware the zipper was broke and am hoping I can fix it because I love it and want my daughter too be able to get some use out of it when she arrives. Any help is helpful. Thanks!