Dead as in browning or yellowing tips? How quickly does this come into the leaves? Could be so many things. My first steps to this issue would be check the roots, make sure there’s no rot or fungus. If so, remove the diseased parts, wash The plant clean under running water, and repot in dry soil (don’t water for a few days). Make sure that plant isn’t getting too much direct sun, some Calathea sunburn easy. They are very very picky, because their leaves are paper thin. Is it sitting too close to your window?

How often do you water? over and underwatering show up most of the time as yellowing leaves, but overwatering can lead to root rot.

Mid none of these are the issue I recommend puttig up pictures. Actually, put me up anyways for more specific and precise advice