Restrictions passcode

I am looking to sell my iPhone 7 Plus and set about to erase all contents and settings. I keyed in my passcode but then was ask to key in my restrictions passcode which I wasn’t able to remember as have not been used once since new. I have attempted 13 times but failed and I guess it would lock out if I keep attempting. I unfortunately do not have a PC or Mac and mini iPad is my only ‘desktop’.

Can anyone advise how I would be able to retrieve my restrictions passcode without the need of PC or Mac, please? Any tips/advice would be much appreciated.. Thank you.