Just follow instructions of masnual to set your MP3 player in "record" mode.
Anything you record is saved in a folder. To play back, select thet particular folser and play bach what you recorded.
Normally MP3 recorders use some kind of "DATE" notation, indicating in filename the date and time you made the recording.
If you don't have the manual, can download from here
Naxa NM 105 Instruction Manual
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