There are a number of reasons you might want to access your save game - maybe you need to move it between devices or maybe we've asked you to send it to us to assist in reviewing a possible bug.
On some devices, it may be possible to access your saves by plugging into a PC, for others you will have to use a file explorer app on your device (Androzip and ES File Explorer are two good free examples). In either case, you will have to navigate to the folder “Documents/Sports Interactive/Football Manager Mobile 2018/normal/games”
The .dat files are your save games, and there can be up to 6 of them. The Manual Saves are named fm_save1.dat through to fm_save4.dat with the name listed after the date on the save. The files hidden.dat and hidden2.dat are the current rolling Automatic Save files on the device (saving alternates between the two, the most recent is on top).