what zcash Android wallet I can export and import the private key ?
Zwallet supports that, also nighthawk (im pretty sure). Zecwallet lite supports that but for its own seed exports, the zecwallet lite desktop version will import normal keys however (I think I tested that but I can’t remember, dont hold me to it )
Guarda has an option under [Wallets management] that allows you to see your Zcash private key.
Edit: I checked and it supports import private key also.
Do you have a transparent, sprout or sapling secret key?