Driver side headlight not working properly

I would start by disconnecting the connector at the headlight in question and have a look at the pins inside the connector. It will either look discolored, or completely burnt to the point that the connector does not seat right. If it is just barely discolored, the pins could be loose from the excess heat and can be cleaned and bent with a pick or pocket screwdriver depending on the size and type of pins. If everything looks normal, swap the left and right headlight bulbs to see if that changes anything, if it bad side is now acting normal, replace the bulb/s. Here is a guide that can help: https://www.2carpros.com/articles/how-to-replace-a-headlight-bulb