How can I maximize the chances I test negative on PCR ?

Basically, I will need to test negative on a PCR:
-17 days after I was initially exposed to covid
-15 days after my symptoms started
-9 days after my symptoms subsided

What are the chances I test negative, and how can I maximize them? I do have double moderna Vax and am young and healthy and my covid case was very mild.

I just need to test negative or im stuck abroad

I'll do whatever to make it more likely to test negative, if pouring alcohol down my nose helps I'll do it