My FLEX-14API Laptop (Lenovo) - Type 81SS is missing a screw in the base at the top left at the hinge. It's causing it to pop up and worsening. Is there any way to get it fixed or get a new screw?

Per page 30 of the Hardware Maintenance Manual for you laptop (see below) all of the screws on the base are M2.0 x 6mm screws.    For the time being, you may want to move one of the 9 remaining screws that secure the bottom case to the hinge position until you get the new screw(s).

As far as getting a replacement, you can get the screw from https://www.metricscrews.us

Below is a link to the one that should fit.    At 29 cents each you may want to get several replacements, because the shipping cost would not change much if any.    

FYI  Nylok is thread locking compound on the thread that keeps the screw from backing out. 

M2x6mm Black Zc Wafer Head Machine Screw w/Nylok #10009  ($0.29/screw + $6.00 shipping)

https://www.metricscrews.us/index.php?main_page=product_info&cPath=98_5_28&products_id=41&zenid=ulca8h3jbml7victrskh8mucf5

Hardware Maintenance Manual  for the Lenovo IdeaPad FLEX-14API

https://download.lenovo.com/consumer/mobiles_pub/c340-14_flex-14_hmm_201903.pdf

Regards,