[help] Pip and different versions of Python

Hey folks! I run Mint 18.3 and I have both Pyhon3.5 and Python3.6 since many devs got crazy with fstring syntactic sugar.
How to deal with Pip module management? The 3.5 version (which is python3) is fine and can import everything as usual, but the 3.6 version (which is python3.6) cannot.
Suggestions?

EDIT: thanks all ^^
I ended up using:
$> python3.6 -m pip install {module I need}