Here are 4 tips that should help you perfect your pronunciation of 'atelier':

• Break 'atelier' down into sounds : [A] + [TEL] + [EE] + [AY] - say it out loud and exaggerate the sounds until you can consistently produce them.
• Record yourself saying 'atelier' in full sentences, then watch yourself and listen. You'll be able to mark your mistakes quite easily.
• Look up tutorials on Youtube on how to pronounce 'atelier'.