How to reset my admin username and password on MacBook ?

Hi I have been trying to install scrivener on my MacBook but after downloading the softer, when prompted to add it to the APPs, Finder asks me for the Admin username and password, which I cannot remember... is the username the same as the one when login in the computer? I had a note with different passwords but they are not accepted. I have installed other apps before - I installed Zoom and Sky.... any tip on retrieving my credentials?

Thanks

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