on android if you cant connect to google play games, first find the path of /android/data/zombie.survival.craft.z
then copy the whole folder of zombie.survival.craft.z and there u have your physical backup...
to make a server backup with your old google account. u need to load your old account if possible to recover your old account using google. then proceed to disconnect your old save to it. then close game and clear cache and datam lastly your backup folder zombie.survival.craft.z copy then paste it to path android/data again..
if you cant recover/connect any save from your old google play games. u need to make a new google account for your new save file. you can edit the connectivity of your games with google play games, go to setting choose you new google account then set it to automatically connect all new games to this profile. then do the clear cache and data again to your game. copy paste the backup folder to the path android/data. then finally your new save file is already backup to server with new google account. hope I help you