Do you mean that your phone isn't allowing you to download apps from Google Play unless you're on wifi? Two possibilities:
1. Go to the main Settings->Data manager->Data Saver, and make sure that either Data Saver is unchecked, or Market is not on the Data Saver list if you want Data Saver to be on. (If Data Saver is on and Market is in the list, it will prevent downloads unless you're on Wifi in order to avoid too much mobile data usage.)
2. Go to Google Play's settings, and make sure Update over Wi-Fi only is unchecked.
Hope that works. In the future, it would be helpful to put a few more details in your original post, so that the many people on this forum who would like to help can answer your questions more accurately!