I have locked myself out of my phone and cannot remember my 6 digit passcode

I have only had my phone for a few days and it is my first iPhone. When I set it up I don't remember putting in a six digit passcode number. I just used the fingerprint option.

During a facetime call 2 days ago the battery went flat. When I plugged in to the charger my phone would not accept my fingerprint. The message on the screen said that I needed to put in my six digit passcode in.

I have tried over the last couple of days putting different combinations in that I think I would have used because I cannot remember setting one up. My phone has now locked me out for an hour (previously it has been for shorter periods).

My phone is a two year old SE first edition which I bought from my friend.