I am unable to reset my screen time passcode

If you used your Apple ID when setting it as requested then you can do this 

If you forgot your Screen Time passcode - Apple Support 

If you failed to do that or chose not to then you must wipe the phone in recovery mode and start again with a blank phone.  

Recovery mode or DFU 

 If you can't update or restore your iPhone or iPod touch – Apple Support (UK) 

You can export as much data as you can to iCloud, turn on iCloud Photos etc before wiping it so you can get it back, but you cannot restore a backup as that will be locked too.