So your parents used Screen Time restrictions, to keep you from downloading apps by yourself – and now you want people to show you how to go behind your parents' backs?
Since your parents know the Screen Time password, but have forgotten how to operate Screen Time, then instead of trying to find a way to go behind their backs, point them to the instructions for Screen Time.
Use Screen Time on your iPhone or iPad - Apple Support
Use parental controls on your child's iPhone and iPad - Apple Support
They can then temporarily relax controls, to allow updates, and then reinstate the controls, if they like. It's their call.
If your parents have set up Family Sharing, this article might be relevant:
Approve what kids buy with Ask to Buy - Apple Support