About the developer version(there is a watermark on the right buttom corner),you can use below method:
1.Connect to your laptop and use adb commands to install.
2.If the app is not big size you can try the bluetooth to transfer the apk file and install it.(our TPS900 is Android system can't use this method in Apple OS)
3.USB disk (TypeC port)
4.TF card,insert the TF card in the slot and install it.The TF card slot is beside the SIM card slots in the Battery compartment.
About the production version of TPS900,you need to sign your app with the softdog or sign your app with your private key,then can use steps 2 or step 3 or step 4 in the above.