We here would always recommend a professional
However
What flavour teenager?
There’s a legal difference in most countries between a 13yo and a 19yo
is that because they can’t do it legally?
They can’t or won’t do subdermal implants?
Is that because of your age?
What city do you live in? People here maybe able to direct you or possibly even help you?
Do you have any medically trained family / friends? Doctor/nurse/ medic / veterinarian
THESE may also help
Watch Installation procedure Guide 1
Watch Installation Procedure Guide 2
Watch Needle insertion angle