Set up custom scans

I’m just starting to use Free Avast 17.6.3625.0. I have two internal & two external drives. I want to schedule a scan on the two internal drives and a separate scheduled scan on two external drives. I can’t figure out how to accomplish that. Would appreciate help. Thank you.

Running Windows 10 64 bit.

https://www.avast.com/faq.php?article=AVKB177#artTitle